網(wǎng)上有一些開源的base64編解碼庫的實現(xiàn)，下面介紹幾個：

cppcodec是一個僅包括頭文件的C++11庫，用于編解碼RFC 4648中指定的base64, base64url, base32, base32hex等，它的License為MIT，源碼在https://github.com/tplgy/cppcodec ,最新發(fā)布版本為v0.2，在windows下需要vs2015及以上才可以正常編譯。

?b64.c是一個C語言實現(xiàn)的base64編解碼庫，它的License為MIT，源碼在https://github.com/littlstar/b64.c。

在https://stackoverflow.com/questions/342409/how-do-i-base64-encode-decode-in-c中給出了一個實現(xiàn)，并給出了一些base64開源庫的性能測試結果。

關于base64的介紹可以參考：https://blog.csdn.net/fengbingchun/article/details/85016088

以下是兩種base64開源庫(b64.c和stackoverflow中給出的)實現(xiàn)的測試代碼：

#include "funset.hpp"
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string>
#include <b64/b64.h>namespace {
// reference: https://stackoverflow.com/questions/342409/how-do-i-base64-encode-decode-in-c
static char encoding_table[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H','I', 'J', 'K', 'L', 'M', 'N', 'O', 'P','Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X','Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f','g', 'h', 'i', 'j', 'k', 'l', 'm', 'n','o', 'p', 'q', 'r', 's', 't', 'u', 'v','w', 'x', 'y', 'z', '0', '1', '2', '3','4', '5', '6', '7', '8', '9', '+', '/' };
static char *decoding_table = NULL;
static int mod_table[] = { 0, 2, 1 };void build_decoding_table()
{decoding_table = (char*)malloc(256);for (int i = 0; i < 64; i++)decoding_table[(unsigned char)encoding_table[i]] = i;
}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 = (char*)malloc(*output_length);if (encoded_data == NULL) return NULL;for (int i = 0, j = 0; i < input_length;) {uint32_t octet_a = i < input_length ? (unsigned char)data[i++] : 0;uint32_t octet_b = i < input_length ? (unsigned char)data[i++] : 0;uint32_t octet_c = i < input_length ? (unsigned char)data[i++] : 0;uint32_t triple = (octet_a << 0x10) + (octet_b << 0x08) + octet_c;encoded_data[j++] = encoding_table[(triple >> 3 * 6) & 0x3F];encoded_data[j++] = encoding_table[(triple >> 2 * 6) & 0x3F];encoded_data[j++] = encoding_table[(triple >> 1 * 6) & 0x3F];encoded_data[j++] = encoding_table[(triple >> 0 * 6) & 0x3F];}for (int i = 0; i < mod_table[input_length % 3]; 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 (decoding_table == NULL) build_decoding_table();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 = (unsigned char*)malloc(*output_length);if (decoded_data == NULL) return NULL;for (int i = 0, j = 0; i < input_length;) {uint32_t sextet_a = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];uint32_t sextet_b = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];uint32_t sextet_c = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];uint32_t sextet_d = data[i] == '=' ? 0 & i++ : decoding_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;
}void base64_cleanup()
{free(decoding_table);
}} // namespaceint test_b64_base64()
{std::string str = "北京ABC123+-*/&@!?0";fprintf(stdout, "str source : %s\n", str.c_str());char* str_en = b64_encode((const unsigned char*)str.c_str(), str.length());fprintf(stdout, "str encode : %s\n", str_en);std::string tmp(str_en);//fprintf(stdout, "str_en length: %d\n", tmp.length());unsigned char* str_de = b64_decode(tmp.c_str(), tmp.length());fprintf(stdout, "str decode : %s\n", str_de);free(str_en);free(str_de);size_t output_length_encode = 0;char* str_en2 = base64_encode((const unsigned char*)str.c_str(), str.length(), &output_length_encode);std::string tmp2(str_en2, output_length_encode);fprintf(stdout, "str encode2: %s\n", tmp2.c_str());size_t output_length_decode = 0;//fprintf(stdout, "output_length_encode: %d, str_en2 length: %d\n", output_length_encode, tmp2.length());unsigned char* str_de2 = base64_decode(str_en2, output_length_encode, &output_length_decode);std::string tmp3((char*)str_de2, output_length_decode);fprintf(stdout, "str decode2: %s\n", tmp3.c_str());free(str_en2);free(str_de2);base64_cleanup();return 0;
}

執(zhí)行結果如下：可見兩種實現(xiàn)的base64編解碼結果一致。

GitHub：?https://github.com/fengbingchun/OpenSSL_Test?

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