I'm fairly new to programming in C. My problem is that I have two implementations of a function and I want to be able to switch between them easily.
Right now I define the two implementations of the function as function_implementation1 and function_implementation1 in the files "funtion_implementation1.h" and "funtion_implementation2.h" respectively. To switch between them I have the following file:
#define IMPLEMENTATION1
#ifdef IMPLEMENTATION_1
#include "funtion_implementation1.h"
#define myFunction function_implementation1
#endif
#ifdef IMPLEMENTATION_2
#include "funtion_implementation2.h"
#define myFunction function_implementation2
#endif
In order to switch from one implementation to the other I just have to change the first line. This approach works, and I was satisfied with it for a while, but now it is bugging me that I have to open this file so often. I have a parameters.h file where I define all my parameters and I would rather choose which implementation to use in that file. Sadly, moving the first line to that file does not work. If I do that myFunction is not defined.
What is the best way to do this?
you should include your parameters file where you use alias, macros, etc:
#include "Parameters.h"
also, all your headers files should start with:
#ifndef __FILE_H__
#define __FILE_H__
// definitions go there
#endif
This prevents nested include of header files
Use preprocessor options, specifically the -D option. If you wanted to use IMPLEMENTATION1, when you are compiling that file on the command line (or in IDE), add -D IMPLEMENTATION1. This defines that macro. Same works for any macro
Related
I have a macro which is used in afile.c and bfile.c (both in module A)
This macro is in aheader.h
Both of these are in different modules/directories and aheader.h module is complied before module A is complied.
Now one way is to do #include "aheader.h" in each of the .c files.
But instead of doing this, is there a way to make some addition in the Makefile (like adding it to the list of headers) for module A,
so that aheader.h is picked for everywhere the macro is used?
#include "aheader.h" is the simple and correct thing to do. C has no feature to auto-include headers when a macro is used.
If you insist on doing it in the makefile, you can add -include aheader.h as a compilation flag. It will include it in all files.
It's possible to use the makefile to add this flag only when the macro is found in the C file, by using grep. But it's complicated makefile work, and I think you're better off without it.
I want to include the result of a macro expansion. It seems include only knows <> ""?
This fails:
#define audio sinwave
#ifdef audio
#include audio".c"
/*#include "sinwave.c"*/
#endif
But this works:
#ifdef audio
if(i==0){set_audio((char *)audio);return;}
#endif
You could do something like this:
#define audio audio
#define FF(X) #X
#define F(X) FF(X.c)
#ifdef audio
#include F(audio)
#endif
that is you'd have to append the .c before you place everything into a string. The usual concatenation "audio" ".c" -> "audio.c" of adjacent strings happens in a later compilation phase than preprocessing, so an #include directive cannot deal with this.
No. Preprocessor directives cannot be used like this. You can use macros to concatenate and stringify names, but that's another case. If you need this, you should most probably re-think your design because it's not good enough at the moment.
Maybe it's not clear to me... But I see a few different questions that you're asking...
I think your asking if you can include source files, yes you can, but its not the best idea; see here for a good discussion why.
If you're wondering about including files with "..." vs <...>, the difference is the quotes are when files are in your local directory (or you want to include the path to the file) the <> are for when the file is in your search path.
If you want to stringify the file name, then
Jens Guestedt answer is what you want... But I question the logic behind doing this...
Why not include the .c file in your project normally (add it to your makefile or whatever) then just wrap the code in question (or the while file) in the #ifdef? That's a much more standard way to conditionally compile the code.
I am working on a GLCD library for embedded devices. The idea is to split it into highlevel and lowlevel section. This allows the "user" to just write the lowlevel functions for his display controller, and use the highlevel functions like line-, cricle-, string drawing etc. without rewriting these functions.
To keep things easy, I decided that the user of the library just has to do the following, for example to use a display with SSD1289 controller, in his main.c:
#define LCD_USE_SSD1289
Example file ssd1289_lld.h:
#ifdef LCD_USE_SSD1289
lld_lcdInit(void);
#endif
Example file ssd1289_lld.c:
lld_lcdInit(void) {
// do some stuff for this controller
}
Example file s6d1121_lld.h:
#ifdef LCD_USE_S6D1121
lld_lcdInit(void);
#endif
Example file s6d1121_lld.c:
lld_lcdInit(void) {
// do some stuff for this controller
}
Inside the highlevel file, I'll just do:
#include "drivers/ssd1289_lld.h"
#include "drivers/s6d1121_lld.h"
void lcdInit(void) {
lld_lcdInit();
}
But this does somehow not work:
When I don't do any #define LCD_USE_SSD1289 it does work without any problems
After adding a second driver for a different type of controller, it still work without defining any type, and it also works when I define the wrong controller type.
What am I doing wrong?
Make sure the preprocessor puts the #ifdef LCD_USE_SSD1289 after the #define LCD_USE_SSD1289 area. You said #define LCD_USE_SSD1289 was in the main.c file. You should really use a separate definitions.h file that is #included at the top of ssd1289_lld.h. Hope that helps.
I work on AS/400 which is sometimes non-POSIX. We also need to compile our code on UNIX. We have an issue with something as simple as #include.
On AS/400, we need to write: #include "*LIBL/H/MYLIB"
On UNIX, we need to write #include "MYLIB.H"
At the moment we have this (ugly) block at the top of each C/C++ file:
#ifndef IS_AS400
#include "*LIBL/H/MYLIB"
/* others here */
#else
#include "MYLIB.H"
/* others here */
#endif
We would like a unified macro. Is this possible? I don't know how to write it.
Ideally, the resulting syntax would be: SAFE_INCLUDE("MYLIB") that would expand correctly on each platform.
Please advise.
You can simply #include some separate header in every of your source files containing that ugly #ifndef just once. It's a common practice anyway.
You can define prefixes for your platform as macro. Like
#define STRINGY(STR) #STR
#define SAFE_INCLUDE(HDR) STRINGY(HDR)
#ifndef IS_AS400
#define SAFE_INCLUDE(LIB) STRINGY(*LIBL/H/##LIB)
#else
#define SAFE_INCLUDE(LIB) STRINGY(LIB##.H)
#endif
and you can use this as
#include SAFE_INCLUDE(MYLIB)
There are two better solutions:
Use your Makefiles to properly set a path where compiler looks for includes.
For GCC you add to CFLAGS -I <path> (you can do that multiple times).
Wrap the non-compliant libraries with your own header files.
I use a parser generator here, that unfortunately insists on putting a
#include <some/file.h>
at the top of every generated source file. The header has since long been renamed. While it is no problem forcing the compiler (gcc) to use the new header with -include new/header.h, removing the above directive from every generated file complicates the build-process.
Is there a way to tell gcc to simply ignore some/file.h?
No. You can post-process your generated file - I say: NO!!!
Or you can just add '.' to your system include directories (or whatever your local include path is - make sure it's also a <> system include path).
Then make a 'some' directory and stick your own permanent 'file.h' in there that has 1 line for #include and get rid of your -include.
I'm guess there's some reason that might not work - cause it seems like the more straight forward and understandable thing to do before using -include. Especially since you can comment the pass-through file to explain what's going on.
Replace some/file.h with an empty file.
Why not make a symlink from some/file.h to new/header.h, and remove the -include directive?
Try using preprocessor directives like #if and #ifdef and gcc -DSYMBOL=value command line flag.
In example, if you compile using gcc -DREQUIRE_STDC=1 -o myfile.o myfile.c, and your .c file contains:
#if defined(REQUIRE_STDC) && defined(__STDC__)
#include "some/file.h"
#else
#include "another/file.h"
#endif /* defined(REQUIRE_STDC) && defined(__STDC__) */
It will compile using "some/file.h" if have both STDC and REQUIRE_STDC symbols defined. Also your header may include the proper directive to avoid multiple inclusions of the same file:
#ifndef MY_HEADER_FILE
#define MY_HEADER_FILE 1
/* your C declarations here */
#endif /* MY_HEADER_FILE */
Also, you could the gcc preprocessor manual.
#include <some/file.h>
may start as something like
#ifndef _FILE_H_
#define _FILE_H_
If so, just add #define _FILE_H_ before the #include command and it should ignore it.
I'm not sure whether this is the best solution, though.