Base64编码、解码的实现（一）

#include <stdio.h>

#include <string.h>



typedef unsigned char BYTE;



/*====================================================================

Base64编码函数

btSrc指向被编码的数据缓冲区

iSrcLen被编码的数据的大小（字节）

btRet指向存放Base64编码的数据缓冲区

piRetLen指向存放Base64编码的数据缓冲区的长度

若btRet为NULL函数返回0，piRetLen传回btSrc的Base64编码所需缓冲区的大小

若btRet指向的缓冲区太小，函数返回-1

否则函数返回实际btSrc的Base64编码所需缓冲区的大小

=====================================================================*/

int EncodeBase64(BYTE *btSrc, int iSrcLen, BYTE *btRet, int *piRetLen) //Base64编码

{

int i = 0, j = 0, k = 0 ;

BYTE EncodeBase64Map[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";



i = (iSrcLen+2) / 3 * 4 ; //获取btSrc的Base64编码所需缓冲区的大小

if(btRet != NULL)

{

if(*piRetLen < i) //Base64编码所需缓冲区偏小

return -1 ;

*piRetLen = i ; //*piRetLen返回btSrc的Base64编码的缓冲区大小

}

else

{

*piRetLen = i ;

return 0 ;

}



k = iSrcLen - iSrcLen % 3 ;

for(i=j=0; i<k; i+=3) //编码

{

btRet[j++] = EncodeBase64Map[(btSrc[i]>>2)&0x3F] ;

btRet[j++] = EncodeBase64Map[((btSrc[i]<<4) + (btSrc[i+1]>>4))&0x3F] ;

btRet[j++] = EncodeBase64Map[((btSrc[i+1]<<2) + (btSrc[i+2]>>6))&0x3F] ;

btRet[j++] = EncodeBase64Map[btSrc[i+2]&0x3F] ;

}

k = iSrcLen - k ;

if(1 == k)

{

btRet[j++] = EncodeBase64Map[(btSrc[i]>>2)&0x3F] ;

btRet[j++] = EncodeBase64Map[(btSrc[i]<<4)&0x3F] ;

btRet[j++] = btRet[j] = '=' ;

}

else if(2 == k)

{

btRet[j++] = EncodeBase64Map[(btSrc[i]>>2)&0x3F] ;

btRet[j++] = EncodeBase64Map[((btSrc[i]<<4) + (btSrc[i+1]>>4))&0x3F] ;

btRet[j++] = EncodeBase64Map[(btSrc[i+1]<<2)&0x3F] ;

btRet[j] = '=' ;

}



return ++j ;

}



/*====================================================================

Base64解码函数

btSrc指向被解码的数据缓冲区

iSrcLen被解码的数据的大小（字节）

btRet指向存放Base64解码的数据缓冲区

piRetLen指向存放Base64解码的数据缓冲区的长度

若btRet为NULL函数返回0，piRetLen传回btSrc的Base64解码所需缓冲区的大小

若btRet指向的缓冲区太小，函数返回-1

否则函数返回btSrc的Base64解码所需缓冲区的大小

=====================================================================*/

int DecodeBase64(BYTE *btSrc, int iSrcLen, BYTE *btRet, int *piRetLen) //Base64解码

{

int i = 0, j = 0 ;

BYTE EncodeBase64Map[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

BYTE DecodeBase64Map[256] = {0} ;



for(j = iSrcLen; j>0 && '='==btSrc[j-1]; --j) ; //忽略=号

i = (j/4)*3+(j%4+1)/2; //计算解码后 字符串的长度



if(btRet != NULL)

{

if(*piRetLen < i) //Base64解码所需缓冲区偏小

return -1 ;

*piRetLen = i ; //*piRetLen返回btSrc的Base64解码的缓冲区大小

}

else

{

*piRetLen = i ;

return 0 ;

}



j = sizeof(EncodeBase64Map) ;

for(i=0; i<j; ++i)

DecodeBase64Map[ EncodeBase64Map[i] ] = i ;

for(i=j=0; i<iSrcLen; i+=4)

{

btRet[j++] = DecodeBase64Map[btSrc[i ]] << 2 | DecodeBase64Map[btSrc[i+1]] >> 4 ;

btRet[j++] = DecodeBase64Map[btSrc[i+1]] << 4 | DecodeBase64Map[btSrc[i+2]] >> 2 ;

btRet[j++] = DecodeBase64Map[btSrc[i+2]] << 6 | DecodeBase64Map[btSrc[i+3]] ;

}



return *piRetLen ;

}



int main(void)

{

char str[128]={0} ;

char szTemp[128] = {0} ;

int iRetLen, i ;

printf("Base64编码：/n") ;

scanf("%s", str) ;

iRetLen = sizeof(szTemp) ;

EncodeBase64(str, strlen(str), szTemp, &iRetLen) ;

szTemp[iRetLen] = '/0' ;

printf("%s/n", szTemp) ;

printf("Base64解码：/n") ;

iRetLen = sizeof(szTemp) ;

scanf("%s", szTemp) ;

DecodeBase64(szTemp, strlen(szTemp), str, &iRetLen) ;

str[iRetLen] = '/0' ;

printf("%s/n", str) ;

for(i=0; i<iRetLen; ++i)

printf("%0x ", (unsigned char)(str[i])) ;

return 0 ;

}



另外，可以参考下面的文章：

http://www.vckbase.com/document/viewdoc/?id=1843