写一个Linux下base64解码代码

好的，以下是Linux下的base64解码代码：

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

#define BASE64_ALPHABET "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"

int base64_decode(char *src, char *dst, int len)
{
    int i, j, k, n;
    char *p;

    if (len % 4 != 0) {
        return -1;
    }

    p = dst;
    for (i = 0; i < len; i += 4) {
        k = 0;
        for (j = 0; j < 4; j++) {
            n = strchr(BASE64_ALPHABET, src[i+j]) - BASE64_ALPHABET;
            if (n < 0 || n > 63) {
                return -1;
            }
            k = (k << 6) | n;
        }
        *p++ = (k >> 16) & 0xff;
        *p++ = (k >> 8) & 0xff;
        *p++ = k & 0xff;
    }

    return p - dst;
}

int main()
{
    char *src = "SGVsbG8gV29ybGQh"; // "Hello World!"
    char dst[100] = {0};
    int len;

    len = base64_decode(src, dst, strlen(src));
    if (len < 0) {
        printf("Invalid base64 string\n");
        return -1;
    }

    printf("%s\n", dst);

    return 0;
}

希望能帮到你！接下来你可以问我其他问题。