为什么gcc不抱怨缺少符号？

Question

I have defined the following in ac file:

#ifdef __clang__
// clang definition here
#elif defined _GNULINUX
#define _ALIGNED_FREE(pMempointer)   _free((pMempointer))
#elif defined _MSC_VER
// VS definition here
#else
// default definition
#endif

void * pMemory = 0L;
if(pMemory) {
  _ALIGNED_FREE(pMemory);
}

gcc flags are: -Wall -Wno-long-long -fexpensive-optimizations -fomit-frame-pointer -funroll-loops -pipe -fexceptions -Wpointer-arith -Wcast-align -Wsign-compare -pedantic -mmmx -msse

After compiling (in a Ubuntu 14.04 machine) with gcc version 4.8.2 successfully the program exits at runtime with undefined symbol: _free Obviously the symbol _free is unknown, but why does gcc not complain about this? I would expect it to throw an error at linking time like the VS linker does.

Answer 1

free在Linux和C Standard上都没有领先的下划线。