C/C++ Base64 编码解码实现源码 - Linux

以下是一个简单的 C 语言实现 Base64 编码和解码的代码：

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

static const char base64_table[] = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

char *base64_encode(const unsigned char *data, size_t input_length, size_t *output_length) {
    *output_length = 4 * ((input_length + 2) / 3);

    char *encoded_data = malloc(*output_length);
    if (encoded_data == NULL) return NULL;

    for (size_t i = 0, j = 0; i < input_length;) {
        uint32_t octet_a = i < input_length ? data[i++] : 0;
        uint32_t octet_b = i < input_length ? data[i++] : 0;
        uint32_t octet_c = i < input_length ? data[i++] : 0;

        uint32_t triple = (octet_a << 0x10) + (octet_b << 0x08) + octet_c;

        encoded_data[j++] = base64_table[(triple >> 3 * 6) & 0x3F];
        encoded_data[j++] = base64_table[(triple >> 2 * 6) & 0x3F];
        encoded_data[j++] = base64_table[(triple >> 1 * 6) & 0x3F];
        encoded_data[j++] = base64_table[(triple >> 0 * 6) & 0x3F];
    }

    for (size_t i = 0; i < *output_length % 4; i++) {
        encoded_data[*output_length - 1 - i] = '=';
    }

    return encoded_data;
}

unsigned char *base64_decode(const char *data, size_t input_length, size_t *output_length) {
    if (input_length % 4 != 0) return NULL;

    *output_length = input_length / 4 * 3;
    if (data[input_length - 1] == '=') (*output_length)--;
    if (data[input_length - 2] == '=') (*output_length)--;

    unsigned char *decoded_data = malloc(*output_length);
    if (decoded_data == NULL) return NULL;

    for (size_t i = 0, j = 0; i < input_length;) {
        uint32_t sextet_a = data[i] == '=' ? 0 & i++ : base64_table[data[i++]];
        uint32_t sextet_b = data[i] == '=' ? 0 & i++ : base64_table[data[i++]];
        uint32_t sextet_c = data[i] == '=' ? 0 & i++ : base64_table[data[i++]];
        uint32_t sextet_d = data[i] == '=' ? 0 & i++ : base64_table[data[i++]];

        uint32_t triple = (sextet_a << 3 * 6) + (sextet_b << 2 * 6) + (sextet_c << 1 * 6) + (sextet_d << 0 * 6);

        if (j < *output_length) decoded_data[j++] = (triple >> 2 * 8) & 0xFF;
        if (j < *output_length) decoded_data[j++] = (triple >> 1 * 8) & 0xFF;
        if (j < *output_length) decoded_data[j++] = (triple >> 0 * 8) & 0xFF;
    }

    return decoded_data;
}

int main() {
    const char *input_data = 'Hello, World!';
    size_t input_length = strlen(input_data);

    size_t encoded_length;
    char *encoded_data = base64_encode((unsigned char *) input_data, input_length, &encoded_length);
    printf('Encoded: %s\n', encoded_data);

    size_t decoded_length;
    unsigned char *decoded_data = base64_decode(encoded_data, encoded_length, &decoded_length);
    printf('Decoded: %s\n', decoded_data);

    free(encoded_data);
    free(decoded_data);

    return 0;
}

你可以使用上面的代码来进行 Base64 编码和解码。