popen implicitly declared even though #include <stdio.h> is added

问题

This is tiny snippet of my code.

   #include <stdio.h>
   #include <unistd.h>
   #include <stdlib.h>
   #include <time.h>
   #include <sys/stat.h>
   #include <sys/wait.h>
   #include <sys/types.h>
   #include <string.h>
   #include <sys/types.h>
   #include <sys/socket.h>
   #include <netinet/in.h>
   #include <arpa/inet.h>
    ...

   FILE * pipe;
    ...

   pipe = popen ("ls /tmp -1", "r");
    ...
   pclose(pipe);

---

blarg.c:106: warning: implicit declaration of function ‘popen’

blarg.c:106: warning: assignment makes pointer from integer without a cast

blarg.c:112: warning: implicit declaration of function ‘pclose’

blarg.c:118: warning: assignment makes pointer from integer without a cast

I'm really unsure. I looked up popen and all it requires is stdio.h which is provided. What is missing, or is the problem in the rest of my code (I don't really want to show more code because its an a assignment).

回答1:

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.

回答2:

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

回答3:

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

来源：https://stackoverflow.com/questions/5468326/popen-implicitly-declared-even-though-include-stdio-h-is-added