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c++ base64編解碼使用示例

更新時(shí)間：2014年02月16日 15:56:57 投稿：zxhpj

這篇文章主要介紹了c++的base64編解碼使用示例,需要的朋友可以參考下

base64碼簡(jiǎn)介

Base64是網(wǎng)絡(luò)上最常見的用于傳輸8Bit字節(jié)代碼的編碼方式之一，大家可以查看RFC2045～RFC2049，上面有MIME的詳細(xì)規(guī)范。Base64編碼可用于在HTTP環(huán)境下傳遞較長的標(biāo)識(shí)信息。例如，在Java Persistence系統(tǒng)Hibernate中，就采用了Base64來將一個(gè)較長的唯一標(biāo)識(shí)符（一般為128-bit的UUID）編碼為一個(gè)字符串，用作HTTP表單和HTTP GET URL中的參數(shù)。在其他應(yīng)用程序中，也常常需要把二進(jìn)制數(shù)據(jù)編碼為適合放在URL（包括隱藏表單域）中的形式。此時(shí)，采用Base64編碼具有不可讀性，即所編碼的數(shù)據(jù)不會(huì)被人用肉眼所直接看到。

0. 源數(shù)據(jù)都是8位位寬的數(shù)據(jù)；
1. 相當(dāng)于分組碼，將源數(shù)據(jù)分為3個(gè)一組，每一組共24bits，采用每6位對(duì)應(yīng)一個(gè)編碼碼字，那么3*8bits = 4*6its, 將3個(gè)數(shù)據(jù)映射成4個(gè)數(shù)據(jù)，由于編碼的碼字都是6位長度，換位10進(jìn)制就是0-63，總共有64中可能性，這也是base64名字的來歷；
2. 6bits對(duì)應(yīng)10進(jìn)制數(shù)對(duì)應(yīng)的碼字如最后的表；

C代碼編碼

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

// 全局常量定義
const char * base64char = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
const char padding_char = '=';

/*編碼代碼
* const unsigned char * sourcedata， 源數(shù)組
* char * base64 ，碼字保存
*/
int base64_encode(const unsigned char * sourcedata, char * base64)
{
 int i=0, j=0;
 unsigned char trans_index=0; // 索引是8位，但是高兩位都為0
 const int datalength = strlen((const char*)sourcedata);
 for (; i < datalength; i += 3){
  // 每三個(gè)一組，進(jìn)行編碼
  // 要編碼的數(shù)字的第一個(gè)
  trans_index = ((sourcedata[i] >> 2) & 0x3f);
  base64[j++] = base64char[(int)trans_index];
  // 第二個(gè)
  trans_index = ((sourcedata[i] << 4) & 0x30);
  if (i + 1 < datalength){
   trans_index |= ((sourcedata[i + 1] >> 4) & 0x0f);
   base64[j++] = base64char[(int)trans_index];
  }else{
   base64[j++] = base64char[(int)trans_index];

   base64[j++] = padding_char;

   base64[j++] = padding_char;

   break; // 超出總長度，可以直接break
  }
  // 第三個(gè)
  trans_index = ((sourcedata[i + 1] << 2) & 0x3c);
  if (i + 2 < datalength){ // 有的話需要編碼2個(gè)
   trans_index |= ((sourcedata[i + 2] >> 6) & 0x03);
   base64[j++] = base64char[(int)trans_index];

   trans_index = sourcedata[i + 2] & 0x3f;
   base64[j++] = base64char[(int)trans_index];
  }
  else{
   base64[j++] = base64char[(int)trans_index];

   base64[j++] = padding_char;

   break;
  }
 }

 base64[j] = '\0'; 

 return 0;
}

解碼

包括兩個(gè)函數(shù)：

/** 在字符串中查詢特定字符位置索引
* const char *str ，字符串
* char c，要查找的字符
*/
inline int num_strchr(const char *str, char c) // 
{
 const char *pindex = strchr(str, c);
 if (NULL == pindex){
  return -1;
 }
 return pindex - str;
}
/* 解碼
* const char * base64 碼字
* unsigned char * dedata， 解碼恢復(fù)的數(shù)據(jù)
*/
int base64_decode(const char * base64, unsigned char * dedata)
{
 int i = 0, j=0;
 int trans[4] = {0,0,0,0};
 for (;base64[i]!='\0';i+=4){
  // 每四個(gè)一組，譯碼成三個(gè)字符
  trans[0] = num_strchr(base64char, base64[i]);
  trans[1] = num_strchr(base64char, base64[i+1]);
  // 1/3
  dedata[j++] = ((trans[0] << 2) & 0xfc) | ((trans[1]>>4) & 0x03);

  if (base64[i+2] == '='){
   continue;
  }
  else{
   trans[2] = num_strchr(base64char, base64[i + 2]);
  }
  // 2/3
  dedata[j++] = ((trans[1] << 4) & 0xf0) | ((trans[2] >> 2) & 0x0f);

  if (base64[i + 3] == '='){
   continue;
  }
  else{
   trans[3] = num_strchr(base64char, base64[i + 3]);
  }

  // 3/3
  dedata[j++] = ((trans[2] << 6) & 0xc0) | (trans[3] & 0x3f);
 }

 dedata[j] = '\0';

 return 0;
}

下面是其他網(wǎng)友的補(bǔ)充可以參考一下

核心代碼

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
static const char b64_table[65] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
static const char reverse_table[128] =
{
 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 62, 64, 64, 64, 63,
 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 64, 64, 64, 64, 64, 64,
 64, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,
 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 64, 64, 64, 64, 64,
 64, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40,
 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 64, 64, 64, 64, 64
};

unsigned char *base64_encode(unsigned char *bindata,size_t inlen,unsigned char **out,size_t *outlen)
{
 size_t _outlen = *outlen;
 unsigned char *_out = NULL;
 size_t out_pos = 0;

 if(NULL == *out)
 {
  _outlen = (inlen / 3 + (inlen%3 != 0)) * 4 + 1;
  _out = malloc(_outlen);
 }
 else
 {
  _outlen = *outlen;
  _out = *out;
 }

 memset(_out,'=',_outlen);
 _out[_outlen-1] = 0;

 unsigned int bits_collected = 0;
 unsigned int accumulator = 0;
 for(int i = 0; i < inlen; i++)
 {
  accumulator = (accumulator << 8) | (bindata[i] & 0xffu);
  bits_collected += 8;
  while (bits_collected >= 6)
  {
   bits_collected -= 6;
   _out[out_pos++] = b64_table[(accumulator >> bits_collected) & 0x3fu];
  }
 }

 if(bits_collected >= 6)
 {
  if(NULL == *out)
  {
   free(_out);
  }
  return NULL;
 }

 if (bits_collected > 0)
 {
  // Any trailing bits that are missing.
  accumulator <<= 6 - bits_collected;
  _out[out_pos++] = b64_table[accumulator & 0x3fu];
 }

 *outlen = _outlen;
 *out = _out;
 return _out;
}

unsigned char *base64_decode(unsigned char *bindata,size_t inlen,unsigned char **out,size_t *outlen)
{
 size_t _outlen = *outlen;
 unsigned char *_out = NULL;
 int bits_collected = 0;
 unsigned int accumulator = 0;
 size_t out_pos = 0;

 if(NULL == *out)
 {
  _outlen = inlen;
  _out = malloc(_outlen);
 }
 else
 {
  _outlen = *outlen;
  _out = *out;
 }

 int c = 0;
 for(int i = 0; i < inlen; i++)
 {
  c = bindata[i];
  if (isspace(c) || c == '=')
  {
   // Skip whitespace and padding. Be liberal in what you accept.
   continue;
  }
  if ((c > 127) || (c < 0) || (reverse_table[c] > 63))
  {
   return NULL;
  }
  accumulator = (accumulator << 6) | reverse_table[c];
  bits_collected += 6;
  if (bits_collected >= 8)
  {
   bits_collected -= 8;
   _out[out_pos++] = (char)((accumulator >> bits_collected) & 0xffu);
  }
 }

 *outlen = _outlen;
 *out = _out;
 return _out;
}

int main(int argc,char *argv[])
{
 unsigned char *str = argv[1];
 unsigned char *out = 0;
 size_t len = 0;
 printf("%s\n",base64_encode(str,strlen(str),&out,&len));
 unsigned char *_out = 0;
 size_t _len = 0;
 printf("%s\n",base64_decode(out,strlen(out),&_out,&_len));
 return 0;
}

這篇C語言base64編解碼的文章就介紹到這了，希望大家以后多多支持腳本之家。

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