#define DEBUG 1 - c

I'm trying to have a debugging mode on so if
#define DEBUG 1
I want to printf some variable values and if
#define DEBUG 0
I want them off.
The problem is I have many implementation files and I want this DEBUG variable to be available for the whole project. Right now I need to edit the DEBUG variable in foo1.c, foo2.c, foo3.c which seems tedious and error-prone and there must be a better way. Any suggestions?

When compiling, you should be able to specify an option to your compiler. For example, you can call GCC with the -DDEBUG option.
In this case, you would be better using:
#ifdef DEBUG
#endif
or:
#if defined(DEBUG)
#endif
if this is not the way you're doing it now. I'm surprised that you don't have a global header file for your project. Something along the lines of:
#undef DEBUG
#define DEBUG 1
in a file called "debug.h". In your C programs, you can include this by using #include "debug.h"

Try something like Steve McConnel suggests in section 6 of "Chapter 8: Defensive Programming" from Code Complete 2... Add this to your code:
#ifdef DEBUG
#if (DEBUG > 0) && (DEBUG < 2)
printf("Debugging level 1");
#endif
#if (DEBUG > 1) && (DEBUG < 3)
printf("Debugging level 2");
#endif
#if (DEBUG > n-1) && (DEBUG < n)
printf("Debugging level n");
#endif
#endif
Then when you compile, add this flag (warning: This might be compiler-dependent):
-DDEBUG=m
Or, have a global header that defines these sorts of things, as others have suggested.

As a response to your problem you can also simply invoke the compiler like:
cc -c -DDEBUG=1
or
cc -c -DDEBUG=0
You must delete the "define DEBUG 1/0" in your files - or replace it with:
#ifndef DEBUG
#define DEBUG 0
#endif
Here is what I am using (GCC syntax):
create a file debug.h with the following content and include it in each c file:
#ifdef DEBUG
extern FILE *dbgf;
#define D_MIN 0x00010000 // Minimum level
#define D_MED 0x00020000 // Medium level
#define D_MAX 0x00040000 // Maximum level
#define D_FLUSH 0x00080000 // Usefull by a program crash
#define D_TRACE 0x00100000
#define D_1 0x00000001
...
#define D(msk, fmt, args...) if(msk & dbgmsk) { fprintf(dbgf, "%s:",__FUNCTION__); fprintf(dbgf, fmt, ## args ); if(msk & D_FLUSH) fflush(dbgf); }
#define P(msk, fmt, args...) if(msk & dbgmsk) { fprintf(dbgf, fmt, ## args ); if(msk & D_FLUSH) fflush(dbgf); }
#else
#define D(msk, fmt, args...)
#define P(msk, fmt, args...)
#endif
dbgmsk is variable, which can be global (whole program) or local/static and must be initialized a start. You can define several options for the whole program or for each module. This is better and more flexible than the version with the level variable.
Ex.
module1.c:
#include "debug.h"
static int dbgmsk; // using local dbgmsk
module1_setdbg(int msk) { dbgmsk = msk; D(D_TRACE,"dbgmsk1=%x\n", dbgmsk); }
foo1() { P(D_1, "foo1 function\n" );
....
}
foo2() {}
...
foo3.c
#include "debug.h"
extern int dbgmsk; // using global dbgmsk
Ex. main:
#include "debug.h"
FILE *dbgf;
int dbgmsk = 0; // this is the global dbgmsk
int main() {
dbgf = stderr; // or your logfile
dbgmsk = D_MIN;
module1_setdbg(D_MIN|D_MED|D_TRACE|D_1);
....
}
I'm also storing all dbgmsk variables in a config text file that is read at the program start.

As #person-b says, specify this define as a compiler option, e.g. -D DEBUG
Note though that to simplify this you should change the test in your code from:
#if DEBUG
to:
#ifdef DEBUG
This way you don't have to worry about specifying a 0 or 1 value but can instead rely on it being defined or not.

Put the "#define DEBUG" in "debug.h" and #include that header file in each *.c file.

The suggestion from samoz and Stephen Doyle to check for the existence of a definition for DEBUG rather than its value is a good one. However, if you really want to use DEBUG=0, this is how you can do it: Each time you define the DEBUG flag (i.e., in each file), check for an existing definition:
#ifndef DEBUG
#define DEBUG 1
#endif
Then, when you use the option -DDEBUG=0 with your compiler, the #define line will never be executed.

Try this instead.
In the first file you have that will be included:
#define DEBUG
Then whenever you want to have debug code, do this:
#ifdef DEBUG
do some stuff
#endif
This will also prevent your debugging code from making it into release code.

I personally like
#ifdef DEBUG
#define IFDEBUG if(0)else
#else
#define IFDEBUG if(1)else
#endif

Related

Error compiling metismex in matlab r2013

I have downloaded and succesfully compiled metis 5.0.2 in a win7 x64 pc
and trying to compile metismex.
I compiled metis with Visual Studio 11 (2012) and using the same compiler from within matlab.
After a lot of experimentation with a ton of errors (mainly owed to paths issues from within the libraries) I have reached a point where I dont know how to proceed, since my knowledge on c and c++ is pretty basic.
So, here's the error :
../GKlib/mat_libs/.\stddef.h(16) : error C2054: expected '(' to follow '_SIZE_TYPE__'
../GKlib/mat_libs/.\stddef.h(19) : error C2085: '_WCHAR_TYPE__' : not in formal parameter list
I found out about the inline functions etc, but since the error is within a library and dont exactly know what I should be doing, here I am. So, the error code is produced here :
typedef __SIZE_TYPE__ size_t;
#ifndef __cplusplus
typedef __WCHAR_TYPE__ wchar_t;
#endif
any suggestions on what I should do without messing it up?
(in case I comment out wchar type, I also have the same error on prtdiff_type)
Thanks in advance
P.S: In case it is needed, here's the whole sttdef.h
/* Copyright 2012 The MathWorks, Inc. */
#ifndef _STDDEF_H
#define _STDDEF_H
#ifdef __cplusplus
extern "C" {
#endif
#ifdef __cplusplus
# define NULL (0)
#else
# define NULL ((void *)0)
#endif
typedef __SIZE_TYPE__ size_t;
#ifndef __cplusplus
typedef __WCHAR_TYPE__ wchar_t;
#endif
typedef __PTRDIFF_TYPE__ ptrdiff_t;
#if (! defined(__cplusplus)) || (! defined(PST_GNU))
# define offsetof(type, field) ((size_t) &((type *)0)->field)
#else
# define offsetof(type, field) \
(__offsetof__(reinterpret_cast<size_t> \
(&reinterpret_cast<const volatile char &> \
(static_cast<type *>(0)->field))))
#endif
#ifdef __cplusplus
} /* extern "C" */
#endif
#endif /* _STDDEF_H *
/
Here is a walk-through of what I did. I'm running R2014a with VS2013 on Win8.1 x64.
1) First we compile metis:
Download and extract metis-5.1.0 to some location, say C:\metis-5.1.0
Edit C:\metis-5.1.0\include\metis.h and set #define IDXTYPEWIDTH 64 (for x64 architecture)
Next we generate Visual Studio projects using CMake:
> cd C:\metis-5.1.0
> vsgen -G "Visual Studio 12 2013 Win64"
Before we build the solution, we need to fix a few things first. Some header files are unnecessarily redefining rint function for MSVC (metisbin.h, metislib.h, and gk_arch.h). Remove such lines:
#ifdef __MSC__ /* MSC does not have rint() function */
#define rint(x) ((int)((x)+0.5))
/* MSC does not have INFINITY defined */
#ifndef INFINITY
#define INFINITY FLT_MAX
#endif
#endif
Also in GKlib\gk_externs.h replace all occurrences of __thread with __declspec(thread)
Next open the solution file C:\metis-5.1.0\build\windows\METIS.sln in Visual Stduio, and build ALL_BUILD target (make sure "x64" in "Release" mode is selected).
We are mainly interested in the metis project. Its result should be stored in C:\metis-5.1.0\build\windows\libmetis\Release\metis.lib (a static library).
2) Next we build the MEX-function:
Download metismex and extract it to a folder inside the previous location (C:\metis-5.1.0\metismex-master)
Again we need to fix a few things: first rename metismex.c to metismex.cpp (the C++ compiler is much better than the C compiler in Visual Studio!). Next edit this file and replace: #include <strings.h> with #include <string.h>, and add the following code immediately after it:
#if defined(_WIN32) || defined(_WIN64)
#define snprintf _snprintf
#define vsnprintf _vsnprintf
#define strcasecmp _stricmp
#define strncasecmp _strnicmp
#endif
Finally start MATLAB, and run the following command to compile the MEX-file:
>> cd('C:\metis-5.1.0\metismex-master')
>> mex -O -largeArrayDims -DWIN32 -DMSC -DUSE_GKREGEX -I../GKlib -I../include -I../libmetis metismex.cpp ../build/windows/libmetis/Release/metis.lib
You should now have the final metismex.mexw64
I should say that I know nothing about the library, so I cannot guarantee it gives correct results after all the above modifications. I'm just showing how to get it to compile. The code was written with Linux/OSX in mind, and relies on many POSIX features not intended for Windows. Also the whole 32 vs. 64 bit is a bit messy...

print only if _DEBUG defined: c

I want to print info only if _DEBUG is defined
#define DEBUG(y) y == true ? #define _DEBUG true : #define _DEBUG false
#ifdef _DEBUG
#define Print(s) printf(s);
#endif
Getting Error:
error: '#' is not followed by a macro parameter
Any suggestion how to achieve this with pre-processor directives?
I intend to use it from my main as:
DEBUG(true);
Print("Inside main in debug mode");
You cannot redefine a MACRO at run-time.
Neither you can have a #define inside of another #define, like you try in the first line of your code.
You can do something like this:
#ifdef _DEBUG
#define Print(s) printf("%s", s)
#else
#define Print(s)
#endif
And use it from your main as:
#define _DEBUG
Print("Inside main in debug mode");
#undef _DEBUG
Print("Inside main debug mode off");
If you really need to switch debug on and off at run-time, your can do something like this:
void PrintIf(BOOL dbg, char * msg)
{
if (dbg)
{
printf("%s", msg)
}
}
And use it like this
y = TRUE;
PrintIf(y,"Inside main in debug mode");
y = FALSE;
PrintIf(y,"Inside main debug mode off");
Try this:
#ifdef DEBUG
#define Print(s) printf("%s", s)
#else
#define Print(s)
#endif
Then:
#define DEBUG
Print("Inside main in debug mode");
I intend to use it from my main as:
DEBUG(y);
Print("Inside main in debug mode");
Sorry, but ifdef are compile time (not run-time). You could use a global bool and runtime checking to enable and disable debug.
You can't create preprocessor statements with macros as you are trying to do; it doesn't work and isn't allowed. For conditional printing, see C #define macro for debug printing.
The problem occurs here:
#define DEBUG(y) y == true ? #define _DEBUG true : #define _DEBUG false
When introducing #defines, the definition # occurs at the beginning of the line, not later (although) preprocessors generally allow one or two line indents.) You need to rewrite your #define eliminating the ternary operator simply as:
#ifdef _DEBUG
#define Print(s) printf(s);
#endif
While you may extend you defines with macros, you often introduce additional errors. It is generally better to stick to wrapping your _DEBUG code simply in #ifdef statements:
#ifdef _DEBUG
fprintf (stderr, "your error messages\n"); // using standard printf/fprintf instead of macros
...
#endif /* _DEBUG */
Macros are substituted at preprocessing stage and
#define DEBUG(y) y == true ? #define _DEBUG true : #define _DEBUG false
this statement will be evaluated at compile time.
Conditional operator (ternary operator) are evaluated at compile time. So you are getting this error and # operator must always be used at the beginning of the statement that is the second mistake you are doing.
You can better use it this way
#define DEBUG
printf ("true");
#else
printf ("false");
You can also define this macro dynamically by using the gcc option -D
gcc -D DEBUG filename.c -o outputFile
The first line is incorrect:
#define DEBUG(y) y == true ? #define _DEBUG true : #define _DEBUG false
You cannot use #define inside preprocessor directive (like another #define)
And it does not make sense, since preprocessing happens before the real compilation (so before run time, when your y has some value). Read the cpp preprocessor documentation. Recall that sometimes the preprocessor is even a different program (/lib/cpp) but is today the first phase of most C compilers.
You could ask for the preprocessed form of your source code (e.g. with gcc -C -E source.c > source.i if using GCC) and look at that form with a pager (less source.i) or your editor.

turning off DEBUG macros for a specific function (NDEBUG)

I am using the following macro for printing debug information that I found on the web. It works great.
However, I would like to turn-off debug printing for function A when debugging function B, which calls function A. I tried #define NDEBUG function A #undef NDEBUG but haven't managed to suppress printing in function A.
Any help will be greatly appreciated.
Any suggestions for alternative ways of accomplishing the task is also welcome.
Thanks ~RT
#ifdef NDEBUG
/*
If not debugging, DEBUGPRINT NOTHING.
*/
#define DEBUGPRINT2(...)
#define DEBUGPRINT(_fmt,G ...)
#else
/*
Debugging enabled:
*/
#define WHERESTR "[file %s, line %d]: "
#define WHEREARG __FILE__, __LINE__
#define DEBUGPRINT2(...) fprintf(stderr, __VA_ARGS__)
#define DEBUGPRINT(_fmt, ...) DEBUGPRINT2(WHERESTR _fmt, WHEREARG, __VA_ARGS__)
#endif /* NDEBUG */
maybe you should wrap the trace into a module so that you can turn on/off the tracing dynamically in run-time and in that way you can specifically turn it off for a function call. In release mode you could replace all tracing with empty statements although in my experience I find it good to keep tracing in release mode as well - just in case.
NDEBUG is useful at the time assert.h is included, so #define NDEBUG/#undef NDEBUG later will not do anything.
You can do something like this though:
#if defined(NDEBUG) || !defined(MY_DEBUG)
/*
If not debugging, DEBUGPRINT NOTHING.
*/
#define DEBUGPRINT2(...)
#define DEBUGPRINT(_fmt,G ...)
#else
/*
Debugging enabled:
*/
#define WHERESTR "[file %s, line %d]: "
#define WHEREARG __FILE__, __LINE__
#define DEBUGPRINT2(...) fprintf(stderr, __VA_ARGS__)
#define DEBUGPRINT(_fmt, ...) DEBUGPRINT2(WHERESTR _fmt, WHEREARG, __VA_ARGS__)
#endif /* NDEBUG */
Then, in function A():
...
#undef MY_DEBUG
result = B();
#define MY_DEBUG
...
This will debug B() when it's called from anywhere except from A(). To get debugging, you will need MY_DEBUG to be defined and NDEBUG to be undefined.
Edit: You will need to define MY_DEBUG when you want to compile with debugging, but hopefully you're using make or some other build tool, so this should be easy.

Can you #define a comment in C?

I'm trying to do a debug system but it seems not to work.
What I wanted to accomplish is something like this:
#ifndef DEBUG
#define printd //
#else
#define printd printf
#endif
Is there a way to do that? I have lots of debug messages and I won't like to do:
if (DEBUG)
printf(...)
code
if (DEBUG)
printf(...)
...
No, you can't. Comments are removed from the code before any processing of preprocessing directives begin. For this reason you can't include comment into a macro.
Also, any attempts to "form" a comment later by using any macro trickery are not guaranteed to work. The compiler is not required to recognize "late" comments as comments.
The best way to implement what you want is to use macros with variable arguments in C99 (or, maybe, using the compiler extensions).
A common trick is to do this:
#ifdef DEBUG
#define OUTPUT(x) printf x
#else
#define OUTPUT(x)
#endif
#include <stdio.h>
int main(void)
{
OUTPUT(("%s line %i\n", __FILE__, __LINE__));
return 0;
}
This way you have the whole power of printf() available to you, but you have to put up with the double brackets to make the macro work.
The point of the double brackets is this: you need one set to indicate that it's a macro call, but you can't have an indeterminate number of arguments in a macro in C89. However, by putting the arguments in their own set of brackets they get interpreted as a single argument. When the macro is expanded when DEBUG is defined, the replacement text is the word printf followed by the singl argument, which is actually several items in brackets. The brackets then get interpreted as the brackets needed in the printf function call, so it all works out.
С99 way:
#ifdef DEBUG
#define printd(...) printf(__VA_ARGS__)
#else
#define printd(...)
#endif
Well, this one doesn't require C99 but assumes compiler has optimization turned on for release version:
#ifdef DEBUG
#define printd printf
#else
#define printd if (1) {} else printf
#endif
On some compilers (including MS VS2010) this will work,
#define CMT / ## /
but no grantees for all compilers.
You can put all your debug call in a function, let call it printf_debug and put the DEBUG inside this function.
The compiler will optimize the empty function.
The standard way is to use
#ifndef DEBUG
#define printd(fmt, ...) do { } while(0)
#else
#define printd(fmt, ...) printf(fmt, __VA_ARGS__)
#endif
That way, when you add a semi-colon on the end, it does what you want.
As there is no operation the compiler will compile out the "do...while"
Untested:
Edit: Tested, using it by myself by now :)
#define DEBUG 1
#define printd(fmt,...) if(DEBUG)printf(fmt, __VA_ARGS__)
requires you to not only define DEBUG but also give it a non-zer0 value.
Appendix:
Also works well with std::cout
In C++17 I like to use constexpr for something like this
#ifndef NDEBUG
constexpr bool DEBUG = true;
#else
constexpr bool DEBUG = false;
#endif
Then you can do
if constexpr (DEBUG) /* debug code */
The caveats are that, unlike a preprocessor macro, you are limited in scope. You can neither declare variables in one debug conditional that are accessible from another, nor can they be used at outside function scopes.
You can take advantage of if. For example,
#ifdef debug
#define printd printf
#else
#define printd if (false) printf
#endif
Compiler will remove these unreachable code if you set a optimization flag like -O2. This method also useful for std::cout.
As noted by McKay, you will run into problems if you simply try to replace printd with //. Instead, you could use variadric macros to replace printd with a function that does nothing as in the following.
#ifndef DEBUG
#define printd(...) do_nothing()
#else
#define printd(...) printf(__VA_ARGS__)
#endif
void do_nothing() { ; }
Using a debugger like GDB might help too, but sometimes a quick printf is enough.
I use this construct a lot:
#define DEBUG 1
#if DEBUG
#if PROG1
#define DEBUGSTR(msg...) { printf("P1: "); printf( msg); }
#else
#define DEBUGSTR(msg...) { printf("P2: "); printf( msg); }
#endif
#else
#define DEBUGSTR(msg...) ((void) 0)
#endif
This way I can tell in my console which program is giving which error message... also, I can search easily for my error messages...
Personally, I don't like #defining just part of an expression...
It's been done. I don't recommend it. No time to test but the mechanism is kind of like this:
#define printd_CAT(x) x ## x
#ifndef DEBUG
#define printd printd_CAT(/)
#else
#define printd printf
#endif
This works if your compiler processes // comments in the compiler itself (there's no guarantee like the ANSI guarantee that there are two passes for /* comments).

#define macro for debug printing in C?

Trying to create a macro which can be used for print debug messages when DEBUG is defined, like the following pseudo code:
#define DEBUG 1
#define debug_print(args ...) if (DEBUG) fprintf(stderr, args)
How is this accomplished with a macro?
If you use a C99 or later compiler
#define debug_print(fmt, ...) \
do { if (DEBUG) fprintf(stderr, fmt, __VA_ARGS__); } while (0)
It assumes you are using C99 (the variable argument list notation is not supported in earlier versions). The do { ... } while (0) idiom ensures that the code acts like a statement (function call). The unconditional use of the code ensures that the compiler always checks that your debug code is valid — but the optimizer will remove the code when DEBUG is 0.
If you want to work with #ifdef DEBUG, then change the test condition:
#ifdef DEBUG
#define DEBUG_TEST 1
#else
#define DEBUG_TEST 0
#endif
And then use DEBUG_TEST where I used DEBUG.
If you insist on a string literal for the format string (probably a good idea anyway), you can also introduce things like __FILE__, __LINE__ and __func__ into the output, which can improve the diagnostics:
#define debug_print(fmt, ...) \
do { if (DEBUG) fprintf(stderr, "%s:%d:%s(): " fmt, __FILE__, \
__LINE__, __func__, __VA_ARGS__); } while (0)
This relies on string concatenation to create a bigger format string than the programmer writes.
If you use a C89 compiler
If you are stuck with C89 and no useful compiler extension, then there isn't a particularly clean way to handle it. The technique I used to use was:
#define TRACE(x) do { if (DEBUG) dbg_printf x; } while (0)
And then, in the code, write:
TRACE(("message %d\n", var));
The double-parentheses are crucial — and are why you have the funny notation in the macro expansion. As before, the compiler always checks the code for syntactic validity (which is good) but the optimizer only invokes the printing function if the DEBUG macro evaluates to non-zero.
This does require a support function — dbg_printf() in the example — to handle things like 'stderr'. It requires you to know how to write varargs functions, but that isn't hard:
#include <stdarg.h>
#include <stdio.h>
void dbg_printf(const char *fmt, ...)
{
va_list args;
va_start(args, fmt);
vfprintf(stderr, fmt, args);
va_end(args);
}
You can also use this technique in C99, of course, but the __VA_ARGS__ technique is neater because it uses regular function notation, not the double-parentheses hack.
Why is it crucial that the compiler always see the debug code?
[Rehashing comments made to another answer.]
One central idea behind both the C99 and C89 implementations above is that the compiler proper always sees the debugging printf-like statements. This is important for long-term code — code that will last a decade or two.
Suppose a piece of code has been mostly dormant (stable) for a number of years, but now needs to be changed. You re-enable debugging trace - but it is frustrating to have to debug the debugging (tracing) code because it refers to variables that have been renamed or retyped, during the years of stable maintenance. If the compiler (post pre-processor) always sees the print statement, it ensures that any surrounding changes have not invalidated the diagnostics. If the compiler does not see the print statement, it cannot protect you against your own carelessness (or the carelessness of your colleagues or collaborators). See 'The Practice of Programming' by Kernighan and Pike, especially Chapter 8 (see also Wikipedia on TPOP).
This is 'been there, done that' experience — I used essentially the technique described in other answers where the non-debug build does not see the printf-like statements for a number of years (more than a decade). But I came across the advice in TPOP (see my previous comment), and then did enable some debugging code after a number of years, and ran into problems of changed context breaking the debugging. Several times, having the printing always validated has saved me from later problems.
I use NDEBUG to control assertions only, and a separate macro (usually DEBUG) to control whether debug tracing is built into the program. Even when the debug tracing is built in, I frequently do not want debug output to appear unconditionally, so I have mechanism to control whether the output appears (debug levels, and instead of calling fprintf() directly, I call a debug print function that only conditionally prints so the same build of the code can print or not print based on program options). I also have a 'multiple-subsystem' version of the code for bigger programs, so that I can have different sections of the program producing different amounts of trace - under runtime control.
I am advocating that for all builds, the compiler should see the diagnostic statements; however, the compiler won't generate any code for the debugging trace statements unless debug is enabled. Basically, it means that all of your code is checked by the compiler every time you compile - whether for release or debugging. This is a good thing!
debug.h - version 1.2 (1990-05-01)
/*
#(#)File: $RCSfile: debug.h,v $
#(#)Version: $Revision: 1.2 $
#(#)Last changed: $Date: 1990/05/01 12:55:39 $
#(#)Purpose: Definitions for the debugging system
#(#)Author: J Leffler
*/
#ifndef DEBUG_H
#define DEBUG_H
/* -- Macro Definitions */
#ifdef DEBUG
#define TRACE(x) db_print x
#else
#define TRACE(x)
#endif /* DEBUG */
/* -- Declarations */
#ifdef DEBUG
extern int debug;
#endif
#endif /* DEBUG_H */
debug.h - version 3.6 (2008-02-11)
/*
#(#)File: $RCSfile: debug.h,v $
#(#)Version: $Revision: 3.6 $
#(#)Last changed: $Date: 2008/02/11 06:46:37 $
#(#)Purpose: Definitions for the debugging system
#(#)Author: J Leffler
#(#)Copyright: (C) JLSS 1990-93,1997-99,2003,2005,2008
#(#)Product: :PRODUCT:
*/
#ifndef DEBUG_H
#define DEBUG_H
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif /* HAVE_CONFIG_H */
/*
** Usage: TRACE((level, fmt, ...))
** "level" is the debugging level which must be operational for the output
** to appear. "fmt" is a printf format string. "..." is whatever extra
** arguments fmt requires (possibly nothing).
** The non-debug macro means that the code is validated but never called.
** -- See chapter 8 of 'The Practice of Programming', by Kernighan and Pike.
*/
#ifdef DEBUG
#define TRACE(x) db_print x
#else
#define TRACE(x) do { if (0) db_print x; } while (0)
#endif /* DEBUG */
#ifndef lint
#ifdef DEBUG
/* This string can't be made extern - multiple definition in general */
static const char jlss_id_debug_enabled[] = "#(#)*** DEBUG ***";
#endif /* DEBUG */
#ifdef MAIN_PROGRAM
const char jlss_id_debug_h[] = "#(#)$Id: debug.h,v 3.6 2008/02/11 06:46:37 jleffler Exp $";
#endif /* MAIN_PROGRAM */
#endif /* lint */
#include <stdio.h>
extern int db_getdebug(void);
extern int db_newindent(void);
extern int db_oldindent(void);
extern int db_setdebug(int level);
extern int db_setindent(int i);
extern void db_print(int level, const char *fmt,...);
extern void db_setfilename(const char *fn);
extern void db_setfileptr(FILE *fp);
extern FILE *db_getfileptr(void);
/* Semi-private function */
extern const char *db_indent(void);
/**************************************\
** MULTIPLE DEBUGGING SUBSYSTEMS CODE **
\**************************************/
/*
** Usage: MDTRACE((subsys, level, fmt, ...))
** "subsys" is the debugging system to which this statement belongs.
** The significance of the subsystems is determined by the programmer,
** except that the functions such as db_print refer to subsystem 0.
** "level" is the debugging level which must be operational for the
** output to appear. "fmt" is a printf format string. "..." is
** whatever extra arguments fmt requires (possibly nothing).
** The non-debug macro means that the code is validated but never called.
*/
#ifdef DEBUG
#define MDTRACE(x) db_mdprint x
#else
#define MDTRACE(x) do { if (0) db_mdprint x; } while (0)
#endif /* DEBUG */
extern int db_mdgetdebug(int subsys);
extern int db_mdparsearg(char *arg);
extern int db_mdsetdebug(int subsys, int level);
extern void db_mdprint(int subsys, int level, const char *fmt,...);
extern void db_mdsubsysnames(char const * const *names);
#endif /* DEBUG_H */
Single argument variant for C99 or later
Kyle Brandt asked:
Anyway to do this so debug_print still works even if there are no arguments? For example:
debug_print("Foo");
There's one simple, old-fashioned hack:
debug_print("%s\n", "Foo");
The GCC-only solution shown below also provides support for that.
However, you can do it with the straight C99 system by using:
#define debug_print(...) \
do { if (DEBUG) fprintf(stderr, __VA_ARGS__); } while (0)
Compared to the first version, you lose the limited checking that requires the 'fmt' argument, which means that someone could try to call 'debug_print()' with no arguments (but the trailing comma in the argument list to fprintf() would fail to compile). Whether the loss of checking is a problem at all is debatable.
GCC-specific technique for a single argument
Some compilers may offer extensions for other ways of handling variable-length argument lists in macros. Specifically, as first noted in the comments by Hugo Ideler, GCC allows you to omit the comma that would normally appear after the last 'fixed' argument to the macro. It also allows you to use ##__VA_ARGS__ in the macro replacement text, which deletes the comma preceding the notation if, but only if, the previous token is a comma:
#define debug_print(fmt, ...) \
do { if (DEBUG) fprintf(stderr, fmt, ##__VA_ARGS__); } while (0)
This solution retains the benefit of requiring the format argument while accepting optional arguments after the format.
This technique is also supported by Clang for GCC compatibility.
Why the do-while loop?
What's the purpose of the do while here?
You want to be able to use the macro so it looks like a function call, which means it will be followed by a semi-colon. Therefore, you have to package the macro body to suit. If you use an if statement without the surrounding do { ... } while (0), you will have:
/* BAD - BAD - BAD */
#define debug_print(...) \
if (DEBUG) fprintf(stderr, __VA_ARGS__)
Now, suppose you write:
if (x > y)
debug_print("x (%d) > y (%d)\n", x, y);
else
do_something_useful(x, y);
Unfortunately, that indentation doesn't reflect the actual control of flow, because the preprocessor produces code equivalent to this (indented and braces added to emphasize the actual meaning):
if (x > y)
{
if (DEBUG)
fprintf(stderr, "x (%d) > y (%d)\n", x, y);
else
do_something_useful(x, y);
}
The next attempt at the macro might be:
/* BAD - BAD - BAD */
#define debug_print(...) \
if (DEBUG) { fprintf(stderr, __VA_ARGS__); }
And the same code fragment now produces:
if (x > y)
if (DEBUG)
{
fprintf(stderr, "x (%d) > y (%d)\n", x, y);
}
; // Null statement from semi-colon after macro
else
do_something_useful(x, y);
And the else is now a syntax error. The do { ... } while(0) loop avoids both these problems.
There's one other way of writing the macro which might work:
/* BAD - BAD - BAD */
#define debug_print(...) \
((void)((DEBUG) ? fprintf(stderr, __VA_ARGS__) : 0))
This leaves the program fragment shown as valid. The (void) cast prevents it being used in contexts where a value is required — but it could be used as the left operand of a comma operator where the do { ... } while (0) version cannot. If you think you should be able to embed debug code into such expressions, you might prefer this. If you prefer to require the debug print to act as a full statement, then the do { ... } while (0) version is better. Note that if the body of the macro involved any semi-colons (roughly speaking), then you can only use the do { ... } while(0) notation. It always works; the expression statement mechanism can be more difficult to apply. You might also get warnings from the compiler with the expression form that you'd prefer to avoid; it will depend on the compiler and the flags you use.
TPOP was previously at http://plan9.bell-labs.com/cm/cs/tpop and http://cm.bell-labs.com/cm/cs/tpop but both are now (2015-08-10) broken.
Code in GitHub
If you're curious, you can look at this code in GitHub in my SOQ (Stack
Overflow Questions) repository as files debug.c, debug.h and mddebug.c in the
src/libsoq
sub-directory.
I use something like this:
#ifdef DEBUG
#define D if(1)
#else
#define D if(0)
#endif
Than I just use D as a prefix:
D printf("x=%0.3f\n",x);
Compiler sees the debug code, there is no comma problem and it works everywhere. Also it works when printf is not enough, say when you must dump an array or calculate some diagnosing value that is redundant to the program itself.
EDIT: Ok, it might generate a problem when there is else somewhere near that can be intercepted by this injected if. This is a version that goes over it:
#ifdef DEBUG
#define D
#else
#define D for(;0;)
#endif
For a portable (ISO C90) implementation, you could use double parentheses, like this;
#include <stdio.h>
#include <stdarg.h>
#ifndef NDEBUG
# define debug_print(msg) stderr_printf msg
#else
# define debug_print(msg) (void)0
#endif
void
stderr_printf(const char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
vfprintf(stderr, fmt, ap);
va_end(ap);
}
int
main(int argc, char *argv[])
{
debug_print(("argv[0] is %s, argc is %d\n", argv[0], argc));
return 0;
}
or (hackish, wouldn't recommend it)
#include <stdio.h>
#define _ ,
#ifndef NDEBUG
# define debug_print(msg) fprintf(stderr, msg)
#else
# define debug_print(msg) (void)0
#endif
int
main(int argc, char *argv[])
{
debug_print("argv[0] is %s, argc is %d"_ argv[0] _ argc);
return 0;
}
Here's the version I use:
#ifdef NDEBUG
#define Dprintf(FORMAT, ...) ((void)0)
#define Dputs(MSG) ((void)0)
#else
#define Dprintf(FORMAT, ...) \
fprintf(stderr, "%s() in %s, line %i: " FORMAT "\n", \
__func__, __FILE__, __LINE__, __VA_ARGS__)
#define Dputs(MSG) Dprintf("%s", MSG)
#endif
I would do something like
#ifdef DEBUG
#define debug_print(fmt, ...) fprintf(stderr, fmt, __VA_ARGS__)
#else
#define debug_print(fmt, ...) do {} while (0)
#endif
I think this is cleaner.
According to http://gcc.gnu.org/onlinedocs/cpp/Variadic-Macros.html,
there should be a ## before __VA_ARGS__.
Otherwise, a macro #define dbg_print(format, ...) printf(format, __VA_ARGS__) will not compile the following example: dbg_print("hello world");.
#define debug_print(FMT, ARGS...) do { \
if (DEBUG) \
fprintf(stderr, "%s:%d " FMT "\n", __FUNCTION__, __LINE__, ## ARGS); \
} while (0)
This is what I use:
#if DBG
#include <stdio.h>
#define DBGPRINT printf
#else
#define DBGPRINT(...) /**/
#endif
It has the nice benefit to handle printf properly, even without additional arguments. In case DBG ==0, even the dumbest compiler gets nothing to chew upon, so no code is generated.
So, when using gcc, I like:
#define DBGI(expr) ({int g2rE3=expr; fprintf(stderr, "%s:%d:%s(): ""%s->%i\n", __FILE__, __LINE__, __func__, #expr, g2rE3); g2rE3;})
Because it can be inserted into code.
Suppose you're trying to debug
printf("%i\n", (1*2*3*4*5*6));
720
Then you can change it to:
printf("%i\n", DBGI(1*2*3*4*5*6));
hello.c:86:main(): 1*2*3*4*5*6->720
720
And you can get an analysis of what expression was evaluated to what.
It's protected against the double-evaluation problem, but the absence of gensyms does leave it open to name-collisions.
However it does nest:
DBGI(printf("%i\n", DBGI(1*2*3*4*5*6)));
hello.c:86:main(): 1*2*3*4*5*6->720
720
hello.c:86:main(): printf("%i\n", DBGI(1*2*3*4*5*6))->4
So I think that as long as you avoid using g2rE3 as a variable name, you'll be OK.
Certainly I've found it (and allied versions for strings, and versions for debug levels etc) invaluable.
My favourite of the below is var_dump, which when called as:
var_dump("%d", count);
produces output like:
patch.c:150:main(): count = 0
Credit to #"Jonathan Leffler". All are C89-happy:
Code
#define DEBUG 1
#include <stdarg.h>
#include <stdio.h>
void debug_vprintf(const char *fmt, ...)
{
va_list args;
va_start(args, fmt);
vfprintf(stderr, fmt, args);
va_end(args);
}
/* Call as: (DOUBLE PARENTHESES ARE MANDATORY) */
/* var_debug(("outfd = %d, somefailed = %d\n", outfd, somefailed)); */
#define var_debug(x) do { if (DEBUG) { debug_vprintf ("%s:%d:%s(): ", \
__FILE__, __LINE__, __func__); debug_vprintf x; }} while (0)
/* var_dump("%s" variable_name); */
#define var_dump(fmt, var) do { if (DEBUG) { debug_vprintf ("%s:%d:%s(): ", \
__FILE__, __LINE__, __func__); debug_vprintf ("%s = " fmt, #var, var); }} while (0)
#define DEBUG_HERE do { if (DEBUG) { debug_vprintf ("%s:%d:%s(): HERE\n", \
__FILE__, __LINE__, __func__); }} while (0)
I've been stewing on how to do this for years, and finally come up with a solution. However, I didn't know that there were other solutions here already. First, at difference with Leffler's answer, I don't see his argument that debug prints should always be compiled. I'd rather not have tons of unneeded code executing in my project, when not needed, in cases where I need to test and they might not be getting optimized out.
Not compiling every time might sound worse than it is in actual practice. You do wind up with debug prints that don't compile sometimes, but it's not so hard to compile and test them before finalizing a project. With this system, if you are using three levels of debugs, just put it on debug message level three, fix your compile errors and check for any others before you finalize yer code. (Since of course, debug statements compiling are no guarantee that they are still working as intended.)
My solution provides for levels of debug detail also; and if you set it to the highest level, they all compile. If you've been using a high debug detail level recently, they all were able to compile at that time. Final updates should be pretty easy. I've never needed more than three levels, but Jonathan says he's used nine. This method (like Leffler's) can be extended to any number of levels. The usage of my method may be simpler; requiring just two statements when used in your code. I am, however, coding the CLOSE macro too - although it doesn't do anything. It might if I were sending to a file.
Against the cost the extra step of testing them to see that they will compile before delivery, is that
You must trust them to get optimized out, which admittedly SHOULD happen if you have a sufficient optimization level.
Furthermore, they probably won't if you make a release compile with optimization turned off for testing purposes (which is admittedly rare); and they almost certainly won't at all during debug - thereby executing dozens or hundreds of "if (DEBUG)" statements at runtime; thus slowing execution (which is my principle objection) and less importantly, increasing your executable or dll size; and hence execution and compile times. Jonathan, however, informs me his method can be made to also not compile statements at all.
Branches are actually relatively pretty costly in modern pre-fetching processors. Maybe not a big deal if your app is not a time-critical one; but if performance is an issue, then, yes, a big enough deal that I'd prefer to opt for somewhat faster-executing debug code (and possibly faster release, in rare cases, as noted).
So, what I wanted is a debug print macro that does not compile if it is not to be printed, but does if it is. I also wanted levels of debugging, so that, e.g. if I wanted performance-crucial parts of the code not to print at some times, but to print at others, I could set a debug level, and have extra debug prints kick in. I came across a way to implement debug levels that determined if the print was even compiled or not. I achieved it this way:
DebugLog.h:
// FILE: DebugLog.h
// REMARKS: This is a generic pair of files useful for debugging. It provides three levels of
// debug logging, currently; in addition to disabling it. Level 3 is the most information.
// Levels 2 and 1 have progressively more. Thus, you can write:
// DEBUGLOG_LOG(1, "a number=%d", 7);
// and it will be seen if DEBUG is anything other than undefined or zero. If you write
// DEBUGLOG_LOG(3, "another number=%d", 15);
// it will only be seen if DEBUG is 3. When not being displayed, these routines compile
// to NOTHING. I reject the argument that debug code needs to always be compiled so as to
// keep it current. I would rather have a leaner and faster app, and just not be lazy, and
// maintain debugs as needed. I don't know if this works with the C preprocessor or not,
// but the rest of the code is fully C compliant also if it is.
#define DEBUG 1
#ifdef DEBUG
#define DEBUGLOG_INIT(filename) debuglog_init(filename)
#else
#define debuglog_init(...)
#endif
#ifdef DEBUG
#define DEBUGLOG_CLOSE debuglog_close
#else
#define debuglog_close(...)
#endif
#define DEBUGLOG_LOG(level, fmt, ...) DEBUGLOG_LOG ## level (fmt, ##__VA_ARGS__)
#if DEBUG == 0
#define DEBUGLOG_LOG0(...)
#endif
#if DEBUG >= 1
#define DEBUGLOG_LOG1(fmt, ...) debuglog_log (fmt, ##__VA_ARGS__)
#else
#define DEBUGLOG_LOG1(...)
#endif
#if DEBUG >= 2
#define DEBUGLOG_LOG2(fmt, ...) debuglog_log (fmt, ##__VA_ARGS__)
#else
#define DEBUGLOG_LOG2(...)
#endif
#if DEBUG == 3
#define DEBUGLOG_LOG3(fmt, ...) debuglog_log (fmt, ##__VA_ARGS__)
#else
#define DEBUGLOG_LOG3(...)
#endif
void debuglog_init(char *filename);
void debuglog_close(void);
void debuglog_log(char* format, ...);
DebugLog.cpp:
// FILE: DebugLog.h
// REMARKS: This is a generic pair of files useful for debugging. It provides three levels of
// debug logging, currently; in addition to disabling it. See DebugLog.h's remarks for more
// info.
#include <stdio.h>
#include <stdarg.h>
#include "DebugLog.h"
FILE *hndl;
char *savedFilename;
void debuglog_init(char *filename)
{
savedFilename = filename;
hndl = fopen(savedFilename, "wt");
fclose(hndl);
}
void debuglog_close(void)
{
//fclose(hndl);
}
void debuglog_log(char* format, ...)
{
hndl = fopen(savedFilename,"at");
va_list argptr;
va_start(argptr, format);
vfprintf(hndl, format, argptr);
va_end(argptr);
fputc('\n',hndl);
fclose(hndl);
}
Using the macros
To use it, just do:
DEBUGLOG_INIT("afile.log");
To write to the log file, just do:
DEBUGLOG_LOG(1, "the value is: %d", anint);
To close it, you do:
DEBUGLOG_CLOSE();
although currently this isn't even necessary, technically speaking, as it does nothing. I'm still using the CLOSE right now, however, in case I change my mind about how it works, and want to leave the file open between logging statements.
Then, when you want to turn on debug printing, just edit the first #define in the header file to say, e.g.
#define DEBUG 1
To have logging statements compile to nothing, do
#define DEBUG 0
If you need info from a frequently executed piece of code (i.e. a high level of detail), you may want to write:
DEBUGLOG_LOG(3, "the value is: %d", anint);
If you define DEBUG to be 3, logging levels 1, 2 & 3 compile. If you set it to 2, you get logging levels 1 & 2. If you set it to 1, you only get logging level 1 statements.
As to the do-while loop, since this evaluates to either a single function or nothing, instead of an if statement, the loop is not needed. OK, castigate me for using C instead of C++ IO (and Qt's QString::arg() is a safer way of formatting variables when in Qt, too — it's pretty slick, but takes more code and the formatting documentation isn't as organized as it might be - but still I've found cases where its preferable), but you can put whatever code in the .cpp file you want. It also might be a class, but then you would need to instantiate it and keep up with it, or do a new() and store it. This way, you just drop the #include, init and optionally close statements into your source, and you are ready to begin using it. It would make a fine class, however, if you are so inclined.
I'd previously seen a lot of solutions, but none suited my criteria as well as this one.
It can be extended to do as many levels as you like.
It compiles to nothing if not printing.
It centralizes IO in one easy-to-edit place.
It's flexible, using printf formatting.
Again, it does not slow down debug runs, whereas always-compiling debug prints are always executed in debug mode. If you are doing computer science, and not easier to write information processing, you may find yourself running a CPU-consuming simulator, to see e.g. where the debugger stops it with an index out of range for a vector. These run extra-slowly in debug mode already. The mandatory execution of hundreds of debug prints will necessarily slow such runs down even further. For me, such runs are not uncommon.
Not terribly significant, but in addition:
It requires no hack to print without arguments (e.g. DEBUGLOG_LOG(3, "got here!");); thus allowing you to use, e.g. Qt's safer .arg() formatting. It works on MSVC, and thus, probably gcc. It uses ## in the #defines, which is non-standard, as Leffler points out, but is widely supported. (You can recode it not to use ## if necessary, but you will have to use a hack such as he provides.)
Warning: If you forget to provide the logging level argument, MSVC unhelpfully claims the identifier is not defined.
You might want to use a preprocessor symbol name other than DEBUG, as some source also defines that symbol (eg. progs using ./configure commands to prepare for building). It seemed natural to me when I developed it. I developed it in an application where the DLL is being used by something else, and it's more convent to send log prints to a file; but changing it to vprintf() would work fine, too.
I hope this saves many of you grief about figuring out the best way to do debug logging; or shows you one you might prefer. I've half-heartedly been trying to figure this one out for decades. Works in MSVC 2012 & 2015, and thus probably on gcc; as well as probably working on many others, but I haven't tested it on them.
I mean to make a streaming version of this one day, too.
Note: Thanks go to Leffler, who has cordially helped me format my message better for StackOverflow.
#define PRINT_LOG(str_format, ...) { \
time_t curtime=time (NULL); \
struct tm *ltm = localtime (&curtime); \
printf("[%d-%02d-%02d %02d:%02d:%02d] " str_format, \
ltm->tm_year + 1900, ltm->tm_mon + 1, ltm->tm_mday, \
ltm->tm_hour, ltm->tm_min, ltm->tm_sec, ##__VA_ARGS__); \
}
PRINT_LOG("[%d] Serving client, str=%s, number=%d\n", getpid(), "my str", 10);
I believe this variation of the theme gives debug categories without the need to have a separate macro name per category.
I used this variation in an Arduino project where program space is limited to 32K and dynamic memory is limited to 2K. The addition of debug statements and trace debug strings quickly uses up space. So it is essential to be able to limit the debug trace that is included at compile time to the minimum necessary each time the code is built.
debug.h
#ifndef DEBUG_H
#define DEBUG_H
#define PRINT(DEBUG_CATEGORY, VALUE) do { if (DEBUG_CATEGORY & DEBUG_MASK) Serial.print(VALUE);} while (0);
#endif
calling .cpp file
#define DEBUG_MASK 0x06
#include "Debug.h"
...
PRINT(4, "Time out error,\t");
...
If you don't care that the output goes to stdout, you can use this:
int doDebug = DEBUG; // Where DEBUG may be supplied in compiler command
#define trace if (doDebug) printf
trace("whatever %d, %i\n", arg1, arg2);

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