popen implicitly declared even though #include is added

Question

This is tiny snippet of my code.

   #include 
   #include 
   #include 
   #include 
   #include         


        

Answer 1

Replace -std=c99 or -std=c11 etc with -std=gnu99 or -std=gnu11.

Answer 2

I put the prototypes of popen and pclose at the top of my code. It seemed to have settled the problem.

Answer 3

As the man page says:

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

popen(), pclose(): _POSIX_C_SOURCE >= 2 || _XOPEN_SOURCE || _BSD_SOURCE
|| _SVID_SOURCE

So you should #define _BSD_SOURCE or one of the others before #includeing stdio.h.