Set variable from makefile?

This is a discussion on Set variable from makefile? within the C Programming forums, part of the General Programming Boards category; I'm using autotools (for the first time) to generate a makefile and all the other things that the GNU autotools ...

  1. #1
    spurious conceit MK27's Avatar
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    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?
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    You can use -D to define things from the command line. (Where in this case, "command line" = "makefile".)

  3. #3
    spurious conceit MK27's Avatar
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    Quote Originally Posted by tabstop View Post
    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.
    Last edited by MK27; 01-30-2009 at 02:18 PM.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  4. #4
    Registered User
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    You probably need escaped double quotes: -DX=\"this\"

  5. #5
    spurious conceit MK27's Avatar
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    Quote Originally Posted by root4 View Post
    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
    Last edited by MK27; 01-30-2009 at 03:23 PM.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

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