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

c srand
Chathura Dodamgoda picture Chathura Dodamgoda · Mar 17, 2013 · Viewed 60.9k times · Source

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

Paul R picture Paul R · Mar 17, 2013

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));

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