C言語はbase64エンコーディングとデコーディングを実装します

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

const char BASE64_CHAR[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
//编码
char *base64_encode(const unsigned char *src, size_t len) {
    
    
    char *out = NULL;
    size_t i, j;
    const unsigned char *p = src;

    out = (char *) malloc(len * 4 / 3 + 4);
    if (out == NULL) {
    
    
        return NULL;
    }

    for (i = 0, j = 0; i < len; i += 3, j += 4) {
    
    
        unsigned int val = p[i] << 16 | (i + 1 < len ? p[i + 1] << 8 : 0) | (i + 2 < len ? p[i + 2] : 0);

        out[j + 0] = BASE64_CHAR[(val >> 18) & 0x3F];
        out[j + 1] = BASE64_CHAR[(val >> 12) & 0x3F];
        out[j + 2] = (i + 1 < len) ? BASE64_CHAR[(val >> 6) & 0x3F] : '=';
        out[j + 3] = (i + 2 < len) ? BASE64_CHAR[(val >> 0) & 0x3F] : '=';
    }

    out[j] = '\0';

    return out;
}
//解码
int base64_decode(const char* encoded_data, char* decoded_data) {
    
    
    int i, j, k = 0;
    int padding = 0;
    int len = strlen(encoded_data);
    if (len < 4) {
    
    
        return 0;
    }
    if (encoded_data[len - 1] == '=') {
    
    
        padding++;
    }
    if (encoded_data[len - 2] == '=') {
    
    
        padding++;
    }
    int decoded_len = 3 * len / 4 - padding;
    for (i = 0; i < len; i += 4) {
    
    
        int c[4];
        for (j = 0; j < 4; j++) {
    
    
            c[j] = strchr(BASE64_CHAR, encoded_data[i + j]) - BASE64_CHAR;
        }
        decoded_data[k++] = (char)((c[0] << 2) | (c[1] >> 4));
        if (k >= decoded_len) {
    
    
            break;
        }
        decoded_data[k++] = (char)(((c[1] & 0x0f) << 4) | (c[2] >> 2));
        if (k >= decoded_len) {
    
    
            break;
        }
        decoded_data[k++] = (char)(((c[2] & 0x03) << 6) | c[3]);
    }
    return decoded_len;
}

テスト

int main() {
    
    
    
    char *src = "12w3454353rwrewrewdc法国德国的风格";
    char *encode = base64_encode((const unsigned char *) src, strlen(src));
    printf("base64 encode:%s\n", encode);

    char decoded[128];
    int decoded_len = base64_decode(encode, decoded);
    decoded[decoded_len] = '\0';
    printf("base64 decode:%s\n", decoded);


    free(encode);

    return 0;
}

結果

g++ base.cpp
base.cpp: In function 'int main()':
base.cpp:66:17: warning: deprecated conversion from string constant to 'char*' [-Wwrite-strings]
     char *src = "12w3454353rwrewrewdc法国德国的风格";
                 ^
a
base64 encode:MTJ3MzQ1NDM1M3J3cmV3cmV3ZGO3qLn6tcK5+rXEt+e48Q==
base64 decode:12w3454353rwrewrewdc法国德国的风格