Thread: Set variable from makefile?

I'm using autotools (for the first time) to generate a makefile and all the other things that the GNU autotools do. Something I wrote is supposed to be included in an upcoming release of a major linux distro so I need to get this stuff right.

Anyway, the program needs to makes use of some external files (eg, images) that I figure will go in INSTALLDIR/share/myapp/. Up until now, the exact location of the files was always known prior to compile, so I just used this:

Code:

#define FILEPATH /usr/local/share/myapp

Since INSTALLDIR won't be determined until compile time (by "configure"), how can I adjust the source code so that FILEPATH will be correct?

Originally Posted by tabstop

You can use -D to define things from the command line. (Where in this case, "command line" = "makefile".)

Hey isn't that neat!

Unfortunately I cannot get it to function for a string literal -- the compiler seems to regard whatever I assign to the "macro" as a variable name and not a value, eg. given

Code:

#include <string.h>

int main() {
	char ptr[64];
	strcpy(ptr,X);
	return 0;
}

gcc -D X=this test.c (or -D X="this" or -DX='this')...
test.c: In function ‘main’:
test.c:5: error: ‘this’ undeclared (first use in this function)

Notice that it's this which is undeclared and not X.

Originally Posted by root4

You probably need escaped double quotes: -DX=\"this\"

Yay, root4!

For posterity, I added this to Makefile.am in src/

Code:

myapp_CFLAGS = -D FILEPATH=\"$(datadir)/@PACKAGE@\"

$(datadir) is already part of the automake deal and defaults to /usr/local/share