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C语言 rand srand rand_r     所属分类 c 浏览量 12
The rand() function computes a sequence of pseudo-random integers in the range of 0 to RAND_MAX
(as defined by the header file  stdlib.h).

The srand() function sets its argument seed as the seed for a new sequence of pseudo-random num-bers to be returned by rand().  
These sequences are repeatable by calling srand() with the same seed value.

If no seed value is provided, the functions are automatically seeded with a value of 1.

The sranddev() function initializes a seed, using the random random number device which returns good random numbers.  
However, the rand() function still remains unsuitable for cryptographic use.

The rand_r() function provides the same functionality as rand().  
A pointer to the context value seed must be supplied by the caller.
     

#include "stdio.h" #include "stdlib.h" int main(int argc, char *argv[]){ if (argc != 2){ printf("seed is needed\n"); exit(EXIT_FAILURE); } int seed = atoi(argv[1]); printf("seed=%d\n",seed); int num = 7; for(int i=0;i < num;i++){ printf("%d\n",rand()); } printf("\n\n"); srand(seed); for(int i=0;i < num;i++){ printf("%d\n",rand()); } printf("\n\n"); seed = seed+1; printf("seed=%d\n",seed); for(int i=0;i < num;i++){ printf("%d \n",rand_r(&seed)); } return 0; }

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