checking for NULL before calling free

Question

Many C code freeing pointers calls:

if (p)
  free(p);

But why? I thought C standard say the free function doesn\'t do anything

Answer 1

I tend to write "if (p) free(p)" a lot, even if I know it's not needed.

I partially blame myself because I learned C the old days when free(NULL) would segfault and I still feel uncomfortable not doing it.

But I also blame the C standard for not being consistent. Would, for example, fclose(NULL) be well defined, I would not have problems in writing:

free(p);
fclose(f);

Which is something that happens very often when cleaning up things. Unfortunately, it seems strange to me to write

free(p);
if (f) fclose(f);

and I end up with

if (p) free(p);
if (f) fclose(f);

I know, it's not a rational reason but that's my case :)