env.i

#ifdef __unix__ /* __unix__ is usually defined by compilers targeting Unix systems */
printf("using linux");
#elif defined _WIN32 /* _WIN32 is usually defined by compilers targeting 32 or 64 bit Windows systems */
printf("using windows");
#endif

-------------------------------------------------------------------------------------------------------

/* Unix systems */

# 1 "hello.c"
# 1 "<built-in>"
# 1 "<command-line>"
# 31 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 32 "<command-line>" 2
# 1 "hello.c"

printf("using linux");

-------------------------------------------------------------------------------------------------------

/* Windows systems */

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



printf("using windows");