rand, rand_r - pseudo-random number generator
#include <stdlib.h> int rand (void); void srand(unsigned int seed); int rand_r(unsigned int *seed);
The rand() function computes a sequence of pseudo-random integers in the range 0 to {RAND_MAX} with a period of at least 232.The srand() function uses the argument as a seed for a new sequence of pseudo-random numbers to be returned by subsequent calls to rand(). If srand() is then called with the same seed value, the sequence of pseudo-random numbers will be repeated. If rand() is called before any calls to srand() are made, the same sequence will be generated as when srand() is first called with a seed value of 1.
The implementation will behave as if no function defined in this document calls rand() or srand.
The rand() interface need not be reentrant.
The rand_r() function computes a sequence of pseudo-random integers in the range 0 to {RAND_MAX}. (The value of the {RAND_MAX} macro will be at least 32767.)
If rand_r() is called with the same initial value for the object pointed to by seed and that object is not modified between successive returns and calls to rand_r(), the same sequence shall be generated.
The rand() function returns the next pseudo-random number in the sequence. The srand() function returns no value.The rand_r() function returns a pseudo-random integer.
No errors are defined.
None.
The drand48() function provides a much more elaborate random number generator.The following code defines a pair of functions which could be incorporated into applications wishing to ensure that the same sequence of numbers is generated across different machines:
static unsigned long int next = 1; int myrand(void) /* RAND_MAX assumed to be 32767 */ { next = next * 1103515245 + 12345; return((unsigned int)(next/65536) % 32768); } void mysrand(unsigned int seed) { next = seed; }
None.
drand48(), srand(), <stdlib.h>.
rand() derived from Issue 1 of the SVID.rand_r() derived from the POSIX Threads Extension (1003.1c-1995).