The GNU C Library - ANSI Random

ANSI C Random Number Functions

This section describes the random number functions that are part of the ANSI C standard.

To use these facilities, you should include the header file `stdlib.h' in your program.

Macro int RAND_MAX

The value of this macro is an integer constant expression that represents the maximum possible value returned by the rand function. In the GNU library, it is 037777777 , which is the largest signed integer representable in 32 bits. In other libraries, it may be as low as 32767 .

Function int rand ()

The rand function returns the next pseudo-random number in the series. The value is in the range from 0 to RAND_MAX .

Function void srand (unsigned int seed)

This function establishes seed as the seed for a new series of pseudo-random numbers. If you call rand before a seed has been established with srand , it uses the value 1 as a default seed.

To produce truly random numbers (not just pseudo-random), do srand (time (0)) .