What is the proper #include for the function '

问题:

I am using the Big Nerd Ranch book Objective-C Programming, and it starts out by having us write in C in the first few chapters. In one of my programs it has me create, I use the sleep function. In the book it told me to put #include <stdlib.h> under the #include <stdio.h> part. This is supposed to get rid of the warning that says "Implicit declaration of function 'sleep' is invalid in C99". But for some reason after I put #include <stdlib.h>, the warning does not go away.. This problem does not stop the program from running fine, but I was just curious on which #include I needed to use!

回答1:

The sleep man page says it is declared in <unistd.h>. Have you included this in your program?

回答2:

sleep is a non-standard function.

• On UNIX, you shall include <unistd.h>.
• On MS-Windows, Sleep is rather from <windows.h>.

In every case, check the documentation.

回答3:

this is what I use for a cross-platform code:

#ifdef _WIN32
#include <Windows.h>
#else
#include <unistd.h>
#endif

int main()
{
  pollingDelay = 100
  //do stuff

  //sleep:
  #ifdef _WIN32
  Sleep(pollingDelay);
  #else
  usleep(pollingDelay*1000);  /* sleep for 100 milliSeconds */
  #endif

  //do stuff again
  return 0;
}

回答4:

For sleep() it should be

#include <unistd.h>

回答5:

sleep(3) is in unistd.h, not stdlib.h. Type man 3 sleep on your command line to confirm for your machine, but I presume you're on a Mac since you're learning Objective-C, and on a Mac, you need unistd.h.