C语言函数可变数量参数实现

直接上代码：

#include <stdio.h>
#include <stdarg.h>

union value {
    char *str_value;
    char char_value;
    int int_value;
    double double_value;
};

void myprintf(char *format, ...)
{
    va_list ap;
    char *p;
    union value v;

    va_start(ap, format);
    for (p = format; *p; p++) {
        if (*p != '%') {
            putchar(*p);
            continue;
        }

        switch (*++p) {
        case 's':
            v.str_value = va_arg(ap, char*);
            printf("%s", v.str_value);
            break;
        case 'c':
            v.char_value = va_arg(ap, int);
            printf("%c", v.char_value);
            break;
        case 'd':
            v.int_value = va_arg(ap, int);
            printf("%d", v.int_value);
            break;
        case 'f':
            v.double_value = va_arg(ap, double);
            printf("%f", v.double_value);
            break;
        }
    }
    va_end(ap);
}

int main()
{
    myprintf("str:%s|char:%c|int:%d|double:%f", "hahaha", 'A', 123, 123.456);
    printf("\n");
}