Gcc preprocessor and pasting

Question

I found this snippet on stackoverflow the other day (thanks for that):

#define PLATFORM 3
#define PASTER(x,y) x ## _ ## y
#define EVALUATOR(x,y)  PASTER(x,y)
#define PLATFORMSPECIFIC(fun) EVALUATOR(fun, PLATFORM)

extern void PLATFORMSPECIFIC(somefunc)(char *x);

Compiled with gcc -E, it results in:

# 1 "xx.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "xx.c"





extern void somefunc_3(char *x);

However:

#define PLATFORM linux
#define PASTER(x,y) x ## _ ## y
#define EVALUATOR(x,y)  PASTER(x,y)
#define PLATFORMSPECIFIC(fun) EVALUATOR(fun, PLATFORM)

extern void PLATFORMSPECIFIC(somefunc)(char *x);

results in:

# 1 "xx.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "xx.c"





extern void somefunc_1(char *x);

What can I do to make this return 'somefunc_linux' ?. Clang seems to do it right, btw.

Answer 1

If you want to use linux as a name, you can change your compiler options to undefine it:

gcc -Ulinux

or to be standards compliant:

gcc -std=c90 -pedantic ... # or -std=c89 or -ansi
gcc -std=c99 -pedantic
gcc -std=c11 -pedantic

See more discussion about why here: Why does the C preprocessor interpret the word "linux" as the constant "1"?