How to define C++ preprocessor variable in Makefile

I have a C++ preprocessor written like this:

  #开发者_JS百科ifdef cpp_variable
   //x+y;
  #endif

Can anyone tell me how to define this in Makefile.

---

This is compiler specific.

GCC uses -Dcpp_variable=VALUE or just -Dcpp_variable

Microsoft's compilers use /D

---

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.

---

Add to Makefile:

CPPFLAGS = -Dcpp_variable

---

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

---

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) $<