How to define C++ preprocessor variable in Makefile

Question

I have a C++ preprocessor written like this:

  #ifdef cpp_variable
   //x+y;
  #endif

Can anyone tell me how to define this in Makefile.

score 52 · Answer 1 · edited Mar 01 '19 at 02:28

52

This is compiler specific.

GCC uses -Dcpp_variable=VALUE or just -Dcpp_variable

Microsoft's compilers use /D

edited Mar 01 '19 at 02:28

Itay Grudev

answered Mar 06 '11 at 22:16

Reed Copsey

score 36 · Answer 2 · edited Aug 18 '17 at 21:58

36

Search your compiler documentation to find how to do that.

For example for g++ the syntax is :

g++ -Dcpp_variable <other stuff>

Which corresponds to adding

CPPFLAGS += -Dcpp_variable

in your makefile.

edited Aug 18 '17 at 21:58

eddi

answered Mar 06 '11 at 22:14

fouronnes

2

Technically, because you can do it from the commandline, it can be done from the makefile -- just put the relevant command in the makefile. (pedantry aside, this comment may not have actually been correct when this answer was written) – Nic May 09 '16 at 12:47

score 12 · Answer 3 · answered Jan 27 '15 at 17:39

12

Add to Makefile:

CPPFLAGS = -Dcpp_variable

answered Jan 27 '15 at 17:39

Peter Tseng

score 5 · Answer 4 · answered Mar 06 '11 at 22:14

5

The syntax is compiler specific, for gcc use the -D option like so: -Dcpp_variable.

answered Mar 06 '11 at 22:14

score 4 · Answer 5 · answered Nov 22 '18 at 06:27

4

Take a variable in Makefile and whatever you need to define in it just add -DXXX. Where XXX in you case is cpp_variable.

For example

COMPILE_OPTS = -DXXX

g++ -c $(COMPILE_OPTS) $<

answered Nov 22 '18 at 06:27

Akhil Pathania

5 Answers5