I am using regex to determine a command line argument has the .dat extension. I am trying the following regex:
#define to_find "^.*\.(dat)?"
For some reason I am getting the warning I stated in the title of this question. First, is this expression correct? I believe it is. Second, if it is correct, how can i get rid of this warning?
I am coding a c program in Xcode and the above #define is in my .h file.
Thanks!
The warning is coming from the C compiler. It is telling you that \. is not a known escape sequence in C. Since this string is going to a regex engine, you need to double-escape the slash, like this:
#define to_find "^.*\\.(dat)?"
This regex would match a string with an optional .dat extension, with dat being optional. However, the dot . is required. If you want the dot to be optional as well, put it inside the parentheses, like this: ^.*(\\.dat)?.
Note that you can avoid escaping the individual metacharacters by enclosing them in square brackets, like this:
#define to_find "^.*([.]dat)?"
You need
#define to_find "^.*\\.(dat)?"
Should do the trick as the \ needs to be escaped for C and not the benefit for regex at this stage
Related
For example:
#include "pathtoheader1/header1.hh"
##include "pathtoheader2/header2.hh"
What is the difference between these two preprocessor directives?
Edit
From what I can tell, the ##include directive, in the context of the program I am working with, will prepend -I flags to the specified include path.
TRICK_CFLAGS += -Imodels
TRICK_CXXFLAGS += -Imodels
The compiler will now look for:
/models/pathtoheader1/header1.hh
instead of
/pathtoheader1/header1.hh
These flags are stored in a .mk file.
Additional Information
I am using NASA's Trick Simulation environment to build a simple 2-body simulation of the earth orbiting the sun. The specific tool I am using is called 'trick-CP', Trick's compilation tool.
https://github.com/nasa/trick
## is the token pasting operator in both the C and C++ preprocessors. It's used to concatenate two arguments.
Since it requires an argument either side, a line starting with it is not syntactically valid, unless it's a continuation of a previous line where that previous line has used the line continuation symbol \ or equivalent trigraph sequence.
Question is about NASA Trick. Trick extends C and C++ language with its own syntax.
From Trick documentation:
Headers files, that supply data-types for user-defined models should be included using ##include . Note the double hash (#).
The second one is a syntax error in C++, and I am pretty sure it is a syntax error in C too. The ## preprocessor operator is only valid inside a preprocessor macro (where it forces token pasting).
Here is what the Trick Documentation says about include:
Include files
There are two types of includes in the S_define file.
Single pound "#" includes.
Include files with a single pound "#" are parsed as they are part of the S_define file. They are treated just as #include files in C or C++ files. These files usually include other sim objects or instantiations as part of the S_define file.
Double pound "#" includes.
Include files with a double pound "##" are not parsed as part of the S_define file. These files are the model header files. They include the model class and structure definitions as well as C prototypes for functions used in the S_define file. Double pound files are copied, minus one pound, to S_source.hh.
Also here is a link to where it talks about it in the Trick documentation: https://nasa.github.io/trick/documentation/building_a_simulation/Simulation-Definition-File
#define DATA_VAR_FILENAME(PROJECT_ID) QUOTES(..\ ## PROJECT_ID ## _data_var.h)
or
#define DATA_VAR_FILENAME(PROJECT_ID) QUOTES(..\##PROJECT_ID##_data_var.h)
for the above line I got below warning
remark: unrecognized token
How to eliminate the warning ?
From the look of it, it looks that you are trying to compose a filename in the preprocessor. This is not possible like that, since the strings that form path names are not tokens for the preprocessor.
Usually there is no need for such a manipulation. String literals are simply concatenated too larger string literals in a later compilation phase. Something like
"../" "my_file.h"
should do the trick.
You also seem to have the difficulty that on your platform \ is the path separator. So you'd have to be careful to escape it in string literals, something like "..\\"
Is there a way to use a preprocessor directive without using the # character in C code?
Can we echo the hash character somehow by using its ASCII etc. equivalents?
Eg: 1 can be echoed by using 'SOH' in the .c source file. Is there a similar hack for
'#'?
You can use the digraph or trigraph equivalent if your compiler supports them (you may need to pass flags to the compiler):
digraph: %:
trigraph: ??=
However, if you're trying to use preprocessor macros to generate preprocessor commands, there's no way to do that.
I have this problem in a header macro expansion under Microsoft C Compiler Preprocessor:
custom.h
.
.
# define _OTHER_INCLUDE_DIR C:\3rdparty\usr\include
# define _3RD_PARTY_HEADERS(headername) <_OTHER_INCLUDE_DIR\headername>
.
.
With a header test:
headertest.h
.
.
#include _3RD_PARTY_HEADERS(stdint.h)
.
Microsoft C preprocessor expand second line like(custom.h):
#include <C:\3rdparty\usr\include\headername>
If I set :
# define _3RD_PARTY_HEADERS(headername) <_OTHER_INCLUDE_DIR\ headername>
The result is:
#include <C:\3rdparty\usr\include\ stdint.h>
How I can fix that?
It looks like you want to juxtapose your directory and your header name. You use ##, like this:
# define _3RD_PARTY_HEADERS(headername) <_OTHER_INCLUDE_DIR\\##headername>
Is there no way to have the \ character sequences to be represented differently? The problem is that this is an escape character for C and C++. C99 explicitly states
If the characters ', \, ", //, or /*
occur in the sequence between the <
and > delimiters, the behavior is
undefined.
(There is a similar phrase for "..." includes.)
and I imagine that for C++ there must be something similar. So maybe you just could use / and the compiler would replace them internally to refer to the correct file on your system.
You know, most compilers have a command-line argument to add to the include path... -I or /I most likely for the Microsoft one. One doesn't usually do what you're doing here, never mind whether or not you can make it work.
Here is an overly simplified version of what I am trying to do:
#define LOGDIRECTORY C:\\logs\\
system("mkdir LOGDIRECTORY");
However the preprocessor, instead of swapping out the defined name is not. Instead the system command actually thinks LOGDIRECTORY is the name, and thus is shooting me errors when starting the program.
I know it's wrong and there must be something I can do with the " marks or other characters to specify what I want, but I can't figure it out. I don't want to hardcode the directory and file names because someone may want to change them in the future and it would be much easier to change a define than the whole function etc.
PS, I am coding this in plain C.
#define LOGDIRECTORY C:\\logs\\
#define DEF2STR(x) #x
system("mkdir " DEF2STR(LOGDIRECTORY));
#define LOGDIRECTORY_WITH_QUOTES "C:\\logs\\"
system("mkdir " LOGDIRECTORY_WITH_QUOTES);
In C, you can do simple string concatenation by writing two string literals with no operator in between. "A" "B" will be converted to "AB" at compile time. You can also use this for splitting a long string to multiple lines.
printf("a very long "
"string indeed");
To convert the define to a proper string, use the pound sign (#) in a macro or skip the whole thing and include the quotes in the define itself.
If you were compiling with GCC, you would have no choice but to wrap the define with quotes since the final trailing backslash would be interpreted as a line continuation character, and if that does not cause an error on its own, the penultimate backslash would likely raise a error. However, if you chose to just get rid of the trailing backslash, you'd still need to use two levels of stringification macros, or your syscal would be "mkdir LOGDIRECTORY". See http://gcc.gnu.org/onlinedocs/cpp/Stringification.html
So the above example would become:
#define LOGDIRECTORY C:\\logs
#define DEF2STR(x) #x
#define STR(x) DEF2STR(x)
system("mkdir " STR(LOGDIRECTORY));