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?

Paul R · Answer 1 · 2013-03-17T07:48:05.313

46

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));

edited Mar 17 '13 at 07:48

answered Mar 17 '13 at 07:09

Paul R

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thanks for answering.. i hv included the stdlib.h ,but after including time.h it gives me another error error: too few arguments to function 'time' – Chathura Dodamgoda Mar 17 '13 at 07:25
the code i included works fine on online compilers like code pad.. im using codeblocks ide on my pc – Chathura Dodamgoda Mar 17 '13 at 07:33
man rand may not work as expected. There are other utilities named rand – jellies Dec 18 '18 at 03:54

Acsor · Answer 2 · 2015-03-18T18:01:20.250

1

Note that time() function uses current time (expressed in seconds since 1970) both in its return value and in its address argument.

edited Mar 18 '15 at 18:01

answered Mar 17 '13 at 08:51

Acsor

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score 0 · Answer 3 · answered Aug 29 '22 at 15:38

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.

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

3 Answers3