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base64代码解决办法

发布时间： 2013-03-27 11:22:42 作者： rapoo

base64代码
关于base64的一种算法的代码，有一句话不太明白，望高手解答：


#include "StdAfx.h"
#include "Base64.h"

char base64EncodeChars[65] ="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";//编码后的字符集
int base64DecodeChars[128]={-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, -1, -1, -1, -1, -1,
-1, -1, -1, 62, -1, -1, -1, 63,
52, 53, 54, 55, 56, 57, 58, 59,
60, 61, -1, -1, -1, -1, -1, -1,
-1, 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, -1, -1, -1, -1, -1,
-1, 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, -1, -1, -1, -1, -1 };//对应ASICC字符的位置

char* base64encode(LPCTSTR str)
{ //加密
char Out[260]={0};
int i = 0, len = strlen(str);
char c1, c2, c3;
while (i < len)
{
c1 = str[i++] & 0xff;
if (i == len)
{
sprintf(Out,"%s%c",Out,base64EncodeChars[c1 >> 2]);
sprintf(Out,"%s%c",Out,base64EncodeChars[(c1 & 0x3) << 4]);
sprintf(Out,"%s==",Out);
break;
}
c2 = str[i++];
if (i == len)
{
sprintf(Out,"%s%c",Out,base64EncodeChars[c1 >> 2]);
sprintf(Out,"%s%c",Out,base64EncodeChars[((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4)]);
sprintf(Out,"%s%c",Out,base64EncodeChars[(c2 & 0xF) << 2]);
sprintf(Out,"%s==",Out);
break;
}
c3 = str[i++];
sprintf(Out,"%s%c",Out,base64EncodeChars[c1 >> 2]);
sprintf(Out,"%s%c",Out,base64EncodeChars[((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4)]);
sprintf(Out,"%s%c",Out,base64EncodeChars[((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6)]);
sprintf(Out,"%s%c",Out,base64EncodeChars[c3 & 0x3F]);
}
return &(*Out);
}
char* utf16to8(LPCTSTR str)
{
char Out[260] ={0};
int i, len;
char c;//char为16位Unicode字符,范围0~0xffff,
len = strlen(str);
for (i = 0; i < len; i++)
{//根据字符的不同范围分别转化
c = str[i];
if ((c >= 0x0001) && (c <= 0x007F))
{
sprintf(Out,"%s%c",Out,str[i]);
}
else if (c > 0x07FF)
{
sprintf(Out,"%s%c",Out,(0xE0 | ((c >> 12) & 0x0F)));
sprintf(Out,"%s%c",Out,(0xE0 | ((c >> 12) & 0x0F)));
sprintf(Out,"%s%c",Out,(0x80 | ((c >> 6) & 0x3F)));


sprintf(Out,"%s%c",Out,(0x80 | ((c >> 0) & 0x3F)));
}
else
{
sprintf(Out,"%s%c",Out,(0xC0 | ((c >> 6) & 0x1F)));
sprintf(Out,"%s%c",Out,(0x80 | ((c >> 0) & 0x3F)));
}
}
return &(*Out);
}

char* base64decode(LPCTSTR str)
{//解密
int c1, c2, c3, c4;
int i=0, len;
char Out[260]={0};
len = strlen(str);
while (i < len)
{
do
{
c1 = base64DecodeChars[str[i++] & 0xff];
} while (i < len && c1 == -1);
if (c1 == -1) break;
do
{
c2 = base64DecodeChars[str[i++] & 0xff];
} while (i < len && c2 == -1);
if (c2 == -1) break;
sprintf(Out,"%s%c",Out,((c1 << 2) | ((c2 & 0x30) >> 4)));
do
{
c3 = str[i++] & 0xff;
if (c3 == 61) return Out;
c3 = base64DecodeChars[c3];
} while (i < len && c3 == -1);
if (c3 == -1) break;
sprintf(Out,"%s%c",Out,((c2 & 0XF) << 4) | ((c3 & 0x3C) >> 2));
do
{
c4 = str[i++] & 0xff;
if (c4 == 61) return Out;
c4 = base64DecodeChars[c4];
} while (i < len && c4 == -1);
if (c4 == -1) break;
sprintf(Out,"%s%c",Out,((c3 & 0x03) << 6) | c4);
}
return &(*Out);
}

char* utf8to16(LPCTSTR str)
{
char Out[260]={0};
int i=0, len;
char c, char2, char3;
len = strlen(str);
while (i < len)
{
c = str[i++];
switch (c >> 4)
{
case 0:
case 1:
case 2:
case 3:
case 4:
case 5:
case 6:
case 7:
sprintf(Out,"%s%c",Out,str[i - 1]);
break;
case 12:
case 13: char2 = str[i++];
sprintf(Out,"%s%c",Out,(((c & 0x1F) << 6) | (char2 & 0x3F)));
break;
case 14: char2 = str[i++];
char3 = str[i++];
sprintf(Out,"%s%c",Out,(((c & 0x0F) << 12) | ((char2 & 0x3F) << 6) | ((char3 & 0x3F) << 0)));
break;
}
}
return &(*Out);
}



其中 base64decode函数里面有一句话，if (c3 == 61) return Out; 这里为什么到61就结束？61对应的字符7，难道有特殊的含义？                                c                  算法                  base64              
[解决办法]
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define BASE64_VALUE_SZ 256
int     base64_value[BASE64_VALUE_SZ];
const unsigned char alphabet[65] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; 
 
class Base64Utility {
public:
    Base64Utility();
    int base64_encode(char *src, int srclen, char *dst, int tail);
    int base64_decode(char *src, int srclen, char *dst);
private:
    void base_64_init(void);
};
Base64Utility::Base64Utility() {
    base_64_init();
}
void Base64Utility::base_64_init(void) {
    int i;

    for (i = 0; i < BASE64_VALUE_SZ; i++) base64_value[i] = -1;
    for (i = 0; i < 64; i++) base64_value[(int) alphabet[i]] = i;
    base64_value['='] = 0;
}
int Base64Utility::base64_encode(char *src, int srclen, char *dst, int tail) {
    int     bits, char_count, len;
    char    *o_char, *lim, *o_lim;
    unsigned char   c;

    if ( !src 
[解决办法]
 !dst) return 0;
    len = srclen;
    lim = src + len;
    o_char = dst;
    o_lim  = dst + (len*4)/3 + 1;
    char_count = 0;
    bits = 0;
    while ( (src < lim) && (o_char < o_lim)) {
        c = *(src++);
        bits += c;
        char_count++;
        if (char_count == 3) {
            *(o_char++) = alphabet[bits >> 18];
            *(o_char++) = alphabet[(bits >> 12) & 0x3f];
            *(o_char++) = alphabet[(bits >> 6) & 0x3f];
            *(o_char++) = alphabet[bits & 0x3f];
            bits = 0;
            char_count = 0;
        } else {
            bits <<= 8;
        }
    }
    if (char_count != 0) {
        bits <<= 16 - (8 * char_count);
        *(o_char++) = alphabet[bits >> 18];
        *(o_char++) = alphabet[(bits >> 12) & 0x3f];
        if (char_count == 1) {
            if (tail) { 
 
                *(o_char++) = '=';
                *(o_char++) = '=';
            }
        } else {
            *(o_char++) = alphabet[(bits >> 6) & 0x3f];
            if (tail) {
                *(o_char++) = '=';
            }
        }
    }
    *(o_char) = 0;
    return strlen(dst);
}
int Base64Utility::base64_decode(char *src, int srclen, char *dst) {
    int j;
    unsigned int k;
    int c, base_result_sz;
    long val;

    if (!src 
[解决办法]
 !dst) return 0;
    base_result_sz = srclen;
    val = c = 0;
    for (j = 0; *src; src++) {
        k = (int) *src % BASE64_VALUE_SZ;
        if (base64_value[k] < 0) continue;
        val <<= 6;
        val += base64_value[k];
        if (++c < 4) continue;
        dst[j++] = (char) (val >> 16);
        dst[j++] = (val >> 8) & 0xff;
        dst[j++] = val & 0xff;
        val = c = 0;
    }
    switch (c) {
        case 2://xxxxxx xx0000
            dst[j++] = (val >> 4) & 0xff;
        break;
        case 3://XXXXXX XXxxxx xxxx00
            dst[j++] = (char) (val >> 10);
            dst[j++] = (val >> 2) & 0xff;
        break;
    }
    return j;
}
Base64Utility b64u;
#define MAXLENS 1024768
#define MAXLEND 1366360
char bufd[MAXLEND];
char bufs[MAXLENS];
FILE *fs,*fd;
int fsize;
int main(int argc,char *argv[]) {
    if (argc<4) {
    USE:
        printf("%s <-e 
 
[解决办法]
-E
[解决办法]
-d> srcfile desfile\n",argv[0]);
        return 1;
    }
    if (stricmp(argv[1],"-e") && stricmp(argv[1],"-d")) goto USE;
    if (0==stricmp(argv[1],"-e")) {
        fs=fopen(argv[2],"rb");
        if (NULL==fs) {
            printf("Can not open file %s!\n",argv[2]);
            return 2;
        }
        fsize=fread(bufs,1,MAXLENS,fs);
        if (fsize<=0) {
            fclose(fs);
            printf("Can not read file %s!\n",argv[2]);
            return 3;
        }
        if (MAXLENS==fsize) printf("Warning: Up to %d bytes.\n",MAXLENS);
        fclose(fs);
        b64u.base64_encode(bufs,fsize,bufd,('E'==argv[2][1]));
        fd=fopen(argv[3],"w");
        if (NULL==fd) {
            printf("Can not create file %s!\n",argv[3]);
            return 4;
        }
        fprintf(fd,"%s",bufd);
        fclose(fd);
    } else {//0==stricmp(argv[1],"-d")
        fd=fopen(argv[2],"rb");
        if (NULL==fd) {
            printf("Can not open file %s!\n",argv[2]);
            return 2;
        }
        fsize=fread(bufd,1,MAXLEND,fd);
        if (fsize<=0) {
            fclose(fd);
            printf("Can not read file %s!\n",argv[2]);
            return 3;
        }
        if (MAXLEND==fsize) printf("Warning: Up to %d bytes.\n",MAXLEND);
        fclose(fd);
        fsize=b64u.base64_decode(bufd,fsize,bufs);
        fs=fopen(argv[3],"wb");
        if (NULL==fs) {
            printf("Can not create file %s!\n",argv[3]); 
 
            return 4;
        }
        if (fsize!=(int)fwrite(bufs,1,fsize,fs)) {
            printf("Write %s error!\n",argv[3]);
            fclose(fs);
            return 5;
        }
        fclose(fs);
    }
    return 0;
}

[解决办法]
base64里一般用'=' (0x3D)(61) 表示结束的。

http://zh.wikipedia.org/wiki/Base64
 







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