Thread: Best way to concatenate #define to "string"

I have some code as such

Code:

#define THE_PATH "/path/to/somthing"
// later on down I do this
some_function (THE_PATH "/image.png");

This is a decent sized app and THE_PATH is something that I dont want to hardcode like this "/path/to/something/image.png"

It compiles, but with a warning of "traditional C rejects string concatenation." It also works fine in the app. (using GCC 3.2.1)

My only question is there a more graceful way of performing this and something that wont produce warnings?

This is for an open source project GrubConf and this change should be making its way to the masses in the next release.

Thanks for any insight you can provide.

I dont want to do strcat because I want it to be concatentated at build time (which i dont think my example does) for performance considerations

What options are you compiling with? My version of gcc 3.2.2 IIRC doesn't complain, as it shouldn't, imho.

I'm using automake/autoconf with no special configure or make options.

I think -Wall or -Wtraditional will show the warning.

But my main concern is that older versions of GCC (2.x) will not compile correctly. I will use a strcat or something if I have to but I would prefer to make this work at compile time. THE_PATH can be modified by configure, so hardcoding is not an option.

Use the preprocessor directive to combine strings.

#define CAT(a,b) a ## b

Quzah.

This is what it looks like now

Code:

#define THE_PATH "/path/tosomething"
#define CAT(a,b) a ## b
some_function (CAT (THE_PATH, "/image.png"));

but I get this warning,
warning: pasting "PACKAGE_PIXMAPS_DIR" and ""/grubconf-app.png"" does not give a valid preprocessing token

Did I do something wrong? or should I disregard the warning? Because the program did compile and run succesfully.

Originally posted by Joe Monti
Did I do something wrong? or should I disregard the warning? Because the program did compile and run succesfully.

Code:

#include <stdio.h>
#define DOG "hello"
#define CAT(a,b) a##b
int main( void )
{
	printf("%s", CAT( DOG, " world\n") );
	return 0;
}

This should compile and run without error.

Quzah.

Yeah .... It compiles and runs without error. I will just disregard the warning.

Thank you!