C预编译宏

/*
 ============================================================================
 Name        : c_test001.c
 Author      : jiftle
 Version     :
 Copyright   : Your copyright notice
 Description : Hello World in C, Ansi-style
 ============================================================================
 */

#include <stdio.h>
#include <stdlib.h>

#define YEAR ((((__DATE__ [7] - '0') * 10 + (__DATE__ [8] - '0')) * 10 \
    + (__DATE__ [9] - '0')) * 10 + (__DATE__ [10] - '0'))

#define MONTH (__DATE__ [2] == 'n' ? 0 \
    : __DATE__ [2] == 'b' ? 1 \
    : __DATE__ [2] == 'r' ? (__DATE__ [0] == 'M' ? 2 : 3) \
    : __DATE__ [2] == 'y' ? 4 \
    : __DATE__ [2] == 'n' ? 5 \
    : __DATE__ [2] == 'l' ? 6 \
    : __DATE__ [2] == 'g' ? 7 \
    : __DATE__ [2] == 'p' ? 8 \
    : __DATE__ [2] == 't' ? 9 \
    : __DATE__ [2] == 'v' ? 10 : 11)

#define DAY ((__DATE__ [4] == ' ' ? 0 : __DATE__ [4] - '0') * 10 \
    + (__DATE__ [5] - '0'))

#define DATE_AS_INT (((YEAR - 2000) * 12 + MONTH) * 31 + DAY)

int main(void) {
    puts("!!!Hello World!!!"); /* prints !!!Hello World!!! */

    printf("%s\n","----------------------------------");
    printf("%-30s = %10d\n","__STDC_HOSTED__",__STDC_HOSTED__);
    printf("%-30s = %10d\n","__STDC_VERSION__",__STDC_VERSION__);
    printf("%-30s = %10d\n","__STDC__",__STDC__);
    printf("%-30s = %10s\n","__DATE__",__DATE__);
    printf("%-30s = %10s\n","__TIME__",__TIME__);

    printf("build time: %d-%02d-%02d %s\n",YEAR, MONTH + 1, DAY,__TIME__);

    return EXIT_SUCCESS;
}

linux下，gcc 运行结果：

----------------------------------
__STDC_HOSTED__ = 1
__STDC_VERSION__ = 201112
__STDC__ = 1
__DATE__ = Jun 22 2017
__TIME__ = 11:08:59
build time: 2017-01-22 11:08:59