공간사랑

/***

#include <stdlib.h>

int rand(void);
void srand(unsigned int seed);

***/

#define MY_DEF_MAX_RANGE 999999

void fnUniqueKeyGenerator(char *sGuidKey)
{
    struct timeval tv_now;
    struct tm      stLocalTimeR;

    char sTemp[64];

    double nTempRandVal = 0;
    double nTempRandMax = 0;
    double nTempRandDiv = 0;
    double nTempRandMul = 0;

    /* get current date time */
    gettimeofday( &tv_now, NULL );

    localtime_r(&tv_now.tv_sec, &stLocalTimeR);

    srand( tv_now.tv_usec );

    nTempRandVal = (double)rand();                /*** 0 ~ RAND_MAX ***/
    nTempRandMax = (double)RAND_MAX;              /*** 2147483647.000000 ***/
    nTempRandDiv = nTempRandVal / nTempRandMax;   /*** 0.000000 ~ 1.000000 ***/
    nTempRandMul = nTempRandDiv * (double)MY_DEF_MAX_RANGE;

    printf("RAND_VAL[%f] RAND_MAX[%f] 0_1_RANGE[%f] 0_X_RANGE[%f]\n", nTempRandVal, nTempRandMax, nTempRandDiv, nTempRandMul );

    memset(sTemp, 0x00, sizeof(sTemp));
    sprintf(sTemp, "%04d%02d%02d%02d%02d%02d%06d%06.0f", stLocalTimeR.tm_year+1900, stLocalTimeR.tm_mon+1, stLocalTimeR.tm_mday, \
                                                     stLocalTimeR.tm_hour, stLocalTimeR.tm_min, stLocalTimeR.tm_sec, \
                                                     (int)tv_now.tv_usec, \
                                                     nTempRandMul );
    strcpy(sGuidKey, sTemp);

    return;
}

실행결과 예시)

RAND_VAL[971492850.000000] RAND_MAX[2147483647.000000] 0_1_RANGE[0.452387] 0_X_RANGE[452386.158965]

20171013144405171148452386 len=26