How to pass macro definition from make command line arguments -D to C source code

Question

I usually pass macro definitions from  make command line  to a  makefile  using the option   -Dname value  The definition is accessible inside the makefile   I also pass macro definitions from the  makefile  to the  source code  using the similar compiler option   -Dname value  supported in many compilers   This definition is accessible in the source code   What I need now  is to allow the user of my makefile to be able to pass arbitrary macro definitions from the  make exe commandline  to  source code  right away  without having to change anything in the makefile   so the user can type   make -f mymakefile mk -SOMEOPTION var 5  then directly the code main c can see var    int main       int i   var

User · Answer

Find the C file and Makefile implementation in below to meet your requirements

foo.c

 main ()
    {
        int a = MAKE_DEFINE;
        printf ("MAKE_DEFINE value:%d\n", a);
    }

Makefile

all:
    gcc -DMAKE_DEFINE=11 foo.c

User · Answer

Call make command this way   make CFLAGS -Dvar 42   And be sure to use   CFLAGS  in your compile command in the Makefile  As  j  rgensen mentioned   putting the variable assignment after the make command will override the CFLAGS value already defined the Makefile   Alternatively you could set -Dvar 42 in another variable than CFLAGS and then reuse this variable in CFLAGS to avoid completely overriding CFLAGS

User · Answer

cat x mak all      echo   OPTION    make -f x mak  OPTION -DPASSTOC 42  echo -DPASSTOC 42 -DPASSTOC 42

User · Answer

Just use a specific variable for that     cat Makefile  all      echo foo   gcc   USER DEFINES  -E -xc -     make USER DEFINES  -Dfoo one  echo foo   gcc -Dfoo one -E -xc -      one    make USER DEFINES  -Dfoo bar  echo foo   gcc -Dfoo bar -E -xc -      bar    make  echo foo   gcc  -E -xc -      foo

User · Answer

Because of low reputation  I cannot comment the accepted answer   I would like to mention the predefined variable CPPFLAGS  It might represent a better fit than CFLAGS or CXXFLAGS  since it is described by the GNU Make manual as      Extra flags to give to the C preprocessor and programs that use it    the C and Fortran compilers     Examples of built-in implicit rules that use CPPFLAGS   n o is made automatically from n c with a recipe of the form      CC    CPPFLAGS    CFLAGS  -c  n o is made automatically from n cc  n cpp  or n C with a recipe of the form      CXX    CPPFLAGS    CXXFLAGS  -c    One would use the command make CPPFLAGS -Dvar 123 to define the desired macro   More info   Variables Used by Implicit Rules Catalogue of Built-In Rules

User · Answer

Call make this way  make CFLAGS -Dvar 42   because you do want to override your Makefile s CFLAGS  and not just the environment  which has a lower priority with regard to Makefile variables

[c] How to pass macro definition from "make" command line arguments (-D) to C source code?

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