Base64 编码和解码源程序（C 语言）

//////////////////////////////////////////////////////////////////////////

//

//    Author:        RainVan(XiaoYunFeng)

//    Description:    Base64 Encode

//

//////////////////////////////////////////////////////////////////////////

int Base64_Enc(char *pcBuf,const char *pcTxt,int nTxtlen)

{

    const unsigned char Base64_EnCoding[65] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

    int nBuflen = 0;

    unsigned char *pt = (unsigned char *)pcTxt;

   

    /* nTxtlen 小于 0，则自行计算 pcTxt 的长度 */

    if( nTxtlen < 0 )

    {

        while( *pt++ ){ nTxtlen++; }

        pt = (unsigned char *)pcTxt;

    }

    if( !nTxtlen ) return 0;

 

    while( nTxtlen > 0 )

    {

        *pcBuf++ = Base64_EnCoding[ ( pt[0] >> 2 ) & 0x3f];

        if( nTxtlen > 2 )

        {

            *pcBuf++ = Base64_EnCoding[((pt[0] & 3) << 4) | (pt[1] >> 4)];

            *pcBuf++ = Base64_EnCoding[((pt[1] & 0xF) << 2) | (pt[2] >> 6)];

            *pcBuf++ = Base64_EnCoding[ pt[2] & 0x3F];

        }

        else

        {

            switch( nTxtlen )

            {

            case 1:

                *pcBuf++ = Base64_EnCoding[(pt[0] & 3) << 4 ];

                *pcBuf++ = '=';

                *pcBuf++ = '=';

                break;

            case 2:

                *pcBuf++ = Base64_EnCoding[((pt[0] & 3) << 4) | (pt[1] >> 4)];

                *pcBuf++ = Base64_EnCoding[((pt[1] & 0x0F) << 2) | (pt[2] >> 6)];

                *pcBuf++ = '=';

            }

        }

        pt += 3;

        nTxtlen -= 3;

        nBuflen += 4;

    }

    *pcBuf = 0;

    return nBuflen;

}

 

//////////////////////////////////////////////////////////////////////////

//

//    Author:        RainVan(XiaoYunFeng)

//    Description:    Base64 Decode

//

//////////////////////////////////////////////////////////////////////////

int Base64_Dec(char *pcBuf,const char *pcTxt,int nTxtlen)

{

    unsigned char ucs[4];

    char *pt = (char *)pcTxt;

    int nBuflen = 0 , nfag = 0 , i = 0;

    /* nTxtlen 小于 0，则自行计算 pcTxt 的长度 */

    if( nTxtlen < 0 )

    {

        while( *pt++ ){ nTxtlen++; }

        pt = (unsigned char *)pcTxt;

    }

    if( !nTxtlen ) return 0;

    while( nTxtlen > 0 )

    {

        nfag = 0;

        for( i=0 ; i<4 ; i++ )

        {

            if (*pt >= 'A' && *pt <= 'Z')

                ucs[i] = *pt - 'A';

            else if (*pt >= 'a' && *pt <= 'z')

                ucs[i] = *pt - 'a' + 26;

            else if (*pt >= '0' && *pt <= '9')

                ucs[i] = *pt - '0' + 52;

            else{

                switch (*pt)

                {

                case '+':

                    ucs[i] = 62;

                    break;

                case '/':

                    ucs[i] = 63;

                    break;

                case '=': /* base64 padding */

                    ucs[i] = 0;

                    break;

                case '\t':

                case '\r':

                case '\n':

                case ' ':

                    nfag++;

                    i--;

                    break;

                case '\0': /* 遇到文尾,直接返回上次字符 buf 的长度 */

                    *pcBuf = 0;

                    return nBuflen;

                    break;

                default:  /* 遇到其它非法字符,直接返回 */

                    *pcBuf = 0;

                    return -1;

                }

            }

            pt++;

        }

        *pcBuf++ = (ucs[0] << 2) | (ucs[1] >> 4);

        *pcBuf++ = (ucs[1] << 4) | (ucs[2] >> 2);

        *pcBuf++ = (ucs[2] << 6) | (ucs[3]);

        nTxtlen -= nfag + 4;

        nBuflen += 3;

    }

    *pcBuf = 0;

    //返回 buf 长度

    return nBuflen;

}