base64解码

　　网络传输经常用base64编码的数据，因此我们需要将其解码成正常字符集合。

　　base64.h

 #ifdef  __cplusplus
 extern "C" {
 #endif

 char * base64_encode( const unsigned char * bindata, char * base64, int binlength );
 int base64_decode( const char * base64, unsigned char * bindata );

 #ifdef  __cplusplus
 }
 #endif

　　base64.c

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include "base64.h"

 #ifndef MAX_PATH
 #define MAX_PATH 256
 #endif

 const char * base64char = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

 char * base64_encode( const unsigned char * bindata, char * base64, int binlength )
 {
     int i, j;
     unsigned char current;

     for ( i = , j =  ; i < binlength ; i +=  )
     {
         current = (bindata[i] >> ) ;
         current &= (unsigned char)0x3F;
         base64[j++] = base64char[(int)current];

         current = ( (unsigned char)(bindata[i] <<  ) ) & ( (unsigned char)0x30 ) ;
         if ( i +  >= binlength )
         {
             base64[j++] = base64char[(int)current];
             base64[j++] = '=';
             base64[j++] = '=';
             break;
         }
         current |= ( (unsigned char)(bindata[i+] >> ) ) & ( (unsigned char) 0x0F );
         base64[j++] = base64char[(int)current];

         current = ( (unsigned char)(bindata[i+] << ) ) & ( (unsigned char)0x3C ) ;
         if ( i +  >= binlength )
         {
             base64[j++] = base64char[(int)current];
             base64[j++] = '=';
             break;
         }
         current |= ( (unsigned char)(bindata[i+] >> ) ) & ( (unsigned char) 0x03 );
         base64[j++] = base64char[(int)current];

         current = ( (unsigned char)bindata[i+] ) & ( (unsigned char)0x3F ) ;
         base64[j++] = base64char[(int)current];
     }
     base64[j] = '\0';
     return base64;
 }

 int base64_decode( const char * base64, unsigned char * bindata )
 {
     int i, j;
     unsigned char k;
     unsigned char temp[];
     for ( i = , j = ; base64[i] != '\0' ; i +=  )
     {
         memset( temp, 0xFF, sizeof(temp) );
         for ( k =  ; k <  ; k ++ )
         {
             if ( base64char[k] == base64[i] )
                 temp[]= k;
         }
         for ( k =  ; k <  ; k ++ )
         {
             if ( base64char[k] == base64[i+] )
                 temp[]= k;
         }
         for ( k =  ; k <  ; k ++ )
         {
             if ( base64char[k] == base64[i+] )
                 temp[]= k;
         }
         for ( k =  ; k <  ; k ++ )
         {
             if ( base64char[k] == base64[i+] )
                 temp[]= k;
         }

         bindata[j++] = ((unsigned char)(((unsigned char)(temp[] << ))&0xFC)) |
                 ((unsigned char)((unsigned char)(temp[]>>)&0x03));
         if ( base64[i+] == '=' )
             break;

         bindata[j++] = ((unsigned char)(((unsigned char)(temp[] << ))&0xF0)) |
                 ((unsigned char)((unsigned char)(temp[]>>)&0x0F));
         if ( base64[i+] == '=' )
             break;

         bindata[j++] = ((unsigned char)(((unsigned char)(temp[] << ))&0xF0)) |
                 ((unsigned char)(temp[]&0x3F));
     }
     return j;
 }