请帮我写一下base64解码 的C语言代码

以下是C语言的base64解码代码：

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

const char base64_table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

int base64_decode(const char *src, unsigned char *dst, int len)
{
    int i, j, k;
    unsigned char c;
    unsigned char *p = dst;

    for (i = 0; i < len; i += 4) {
        k = 0;
        for (j = 0; j < 4; j++) {
            c = src[i + j];
            if (c == '=') {
                k++;
                continue;
            }
            c = strchr(base64_table, c) - base64_table;
            if (c == (unsigned char)-1) {
                return -1;
            }
            switch (j) {
            case 0:
                *p++ = (c << 2);
                break;
            case 1:
                *p++ |= (c >> 4);
                *p++ = (c << 4);
                break;
            case 2:
                *p++ |= (c >> 2);
                *p++ = (c << 6);
                break;
            case 3:
                *p++ |= c;
                break;
            }
        }
        p -= k;
    }

    return p - dst;
}

int main()
{
    const char *src = "SGVsbG8gV29ybGQh";
    unsigned char dst[1024];
    int len;

    len = base64_decode(src, dst, strlen(src));
    if (len < 0) {
        printf("base64_decode failed\n");
        return -1;
    }

    printf("decoded: %.*s\n", len, dst);

    return 0;
}

注意：这只是一个示例代码，实际应用中需要根据具体情况进行修改和优化。