implicit declaration of function 'time' [-Wimplicit-function-declaration]|

Question

Whenever I try to use srand function I get this warning

"implicit declaration of function 'time' [-Wimplicit-function-declaration]|" 

and a windows error report appears when running the compiled file ,
I'm a novice to c programming, I found this on a text book, but it doesn't work for me.

  srand (time());  
  int x= (rand()%10) +1;  
  int y= (rand()%10) +1;  
  printf("\nx=%d,y=%d", x,y); 

What do I need to correct this?

Answer 1

You need to make sure that you #include the right headers, in this case:

#include <stdlib.h>  // rand(), srand()
#include <time.h>    // time()

When in doubt, check the man pages:

$ man rand

$ man time

One further problem: time() requires an argument, which can be NULL , so your call to srand() should be:

srand(time(NULL));

Answer 2

请注意， time()函数在其返回值和地址参数中使用当前时间（自1970年以秒表示）。

Answer 3

I had this issue, and the problem was that in windows you need to include sys/time.h , but in linux you need time.h and I didn't notice.

I fixed this by adding a simple platform check:

#ifdef _WIN32
#include <sys/time.h>
#else
#include <time.h>
#endif

Note that this is for windows and linux, because that's what I needed for my program.