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rand, srand - Íð¿ô¤òÀ¸À®¤¹¤ë´Ø¿ô

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#include <stdlib.h>



int rand(void);



int rand_r(unsigned int *seedp);



void srand(unsigned int seed);

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rand() ¤È srand() ¤Î Linux C Library ÈǤϡ¢ random(3) ¤È srandom(3) ¤Îξ´Ø¿ô¤ÈƱ¤¸Íð¿ôÀ¸À® ¥¢¥ë¥´¥ê¥º¥à¤ò»ÈÍѤ·¤Æ¤¤¤ë¡£¤½¤Î¤¿¤á¡¢²¼°Ì¤Î¥Ó¥Ã¥È¤Ï¾å°Ì¤Î¥Ó¥Ã¥È¤È Ʊ¤¸¤¯¤é¤¤¤Ë¥é¥ó¥À¥à¤Ç¤¢¤ë¡£ ¤·¤«¤·¡¢µìÈǤΠrand() ¤Î¼ÂÁõ¤ä¡¢Â¾¤Î¥·¥¹¥Æ¥à¤Î¸½ºß¤Î¼ÂÁõ¤Ç¤Ï¡¢²¼°Ì¤Î¥Ó¥Ã¥È¤¬¾å°Ì¤Î¥Ó¥Ã¥È¤Û¤É ¥é¥ó¥À¥à¤Ë¤Ê¤Ã¤Æ¤¤¤Ê¤¤¡£°Ü¿¢À­¤ò¹â¤á¤ë¾ì¹ç¤Ç¤â¡¢ÀºÅ٤ι⤤Íð¿ô¤¬É¬Í×¤Ê ¥¢¥×¥ê¥±¡¼¥·¥ç¥ó¤Ç¤Ï¤³¤Î´Ø¿ô¤Ï»ÈÍѤ·¤Æ¤Ï¤¤¤±¤Ê¤¤¡£

Numerical Recipes in C: The Art of Scientific Computing (William H. Press, Brian P. Flannery, Saul A. Teukolsky, William T. Vetterling; New York: Cambridge University Press, 1992 (2nd ed., p. 277)) ¤Ç¤Ï¡¢¼¡¤Î¤è¤¦¤Ê¥³¥á¥ó¥È¤¬¤Ê¤µ¤ì¤Æ¤¤¤ë¡£

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j = 1 + (int) (10.0 * rand() / (RAND_MAX + 1.0));

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j = 1 + (rand() % 10);

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Íð¿ô¤ÎÀ¸À®¤ÏÊ£»¨¤ÊÏÃÂê¤Ç¤¢¤ë¡£Á°½Ò¤Î Numerical Recipes in C ¤Ç¤Ï¼ÂÍÑŪ¤ÊÍð¿ôÀ¸À®¤òÏÀÅÀ¤È¤·¤¿Í¥¤ì¤¿µÄÏÀ¤¬Âè 7 ¾Ï (Íð¿ô) ¤ÇŸ³«¤µ¤ì¤Æ¤¤¤ë¡£

¤è¤êÍýÏÀŪ¤ÊµÄÏÀ¤Ë¤Ä¤¤¤Æ¤Ï Donald E. Knuth ¤Î The Art of Computer Programming, volume 2 (Seminumerical Algorithms), 2nd ed.; Reading, Massachusetts: Addison-Wesley Publishing Company, 1981 ¤ÎÂè 3 ¾Ï (Íð¿ô) ¤ò¸«¤è¡£¤³¤³¤Ç¤Ï¡¢ ¤¿¤¯¤µ¤ó¤Î¼ÂÍÑŪ¤ÊÏÃÂê¤Ë¤Ä¤¤¤Æ¤â¿¼¤¯ÌÖÍ夵¤ì¤Æ¤¤¤ë¡£

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POSIX 1003.1-2003 ¤Ç¤Ï¡¢ rand() ¤È srand() ¤Î¼ÂÁõÎã¤È¤·¤Æ°Ê²¼¤òµó¤²¤Æ¤¤¤ë¡£¤³¤ì¤Ï¡¢°Û¤Ê¤ë£²¤Ä¤Î¥Þ¥·¥ó¤ÇƱ¤¸Íð¿ô·ÏÎó¤¬ É¬Íפʾì¹ç¤Ë¤ÏÊØÍø¤Ç¤¢¤í¤¦¡£

    static unsigned long next = 1;



    /* RAND_MAX ¤ò 32767 ¤È²¾Äê */

    int myrand(void) {

        next = next * 1103515245 + 12345;

        return((unsigned)(next/65536) % 32768);

    }



    void mysrand(unsigned seed) {

        next = seed;

    }

´ØÏ¢¹àÌÜ

drand48(3), random(3)