我正在尝试用 C++ 重写这个 javascript base64 编码例程(请注意它不是标准的 base64,并且在解码字符串的开头有一个 .)。
这是 JS 脚本的示例 - https://jsfiddle.net/km53844e/1/
我在下方发布的 javascript base64 类。
在 JS 脚本中,它正确地将 CcnK 转换为 CMlaKA 。但是,在 C++ 脚本中,它错误地将其转换为 CMlaKr(不确定为什么,可能与 JS 脚本中的其他 NaN 语句有关吗?
或者它可能与 C++ 脚本中的空终止字符串有关?我注意到,如果我删除它,我会得到仍然不正确的 CMlaKs。
我尝试添加以下内容来处理 isnans,但它不起作用。
if (isnan(char_array_4[1])) {
char_array_4[2] = char_array_4[1] = 64;
} else if (isnan(char_array_4[2])) {
char_array_4[3] = 64;
}
C++代码:
std::string base64_encode(unsigned char const* bytes_to_encode, unsigned int in_len) {
std::string ret;
int i = 0;
int j = 0;
unsigned char char_array_3[3];
unsigned char char_array_4[4];
while (in_len--) {
char_array_3[i++] = *(bytes_to_encode++);
if (i == 3) {
char_array_4[0] = char_array_3[0] & 0x3f;
char_array_4[1] = ((char_array_3[0] & 0x0f) << 2) + ((char_array_3[1] & 0xc0) >> 6);
char_array_4[2] = ((char_array_3[1] & 0x03) << 4) + ((char_array_3[2] & 0xf0) >> 4);
char_array_4[3] = (char_array_3[2] & 0xfc) >> 2;
if (isnan(char_array_4[1])) {
char_array_4[2] = char_array_4[1] = 64;
} else if (isnan(char_array_4[2])) {
char_array_4[3] = 64;
}
for(i = 0; (i < 4) ; i++)
ret += base64_chars[char_array_4[i]];
i = 0;
}
}
if (i)
{
for(j = i; j < 3; j++)
char_array_3[j] = '\0';
char_array_4[0] = char_array_3[0] & 0x3f;
char_array_4[1] = ((char_array_3[0] & 0x0f) << 2) + ((char_array_3[1] & 0xc0) >> 6);
char_array_4[2] = ((char_array_3[1] & 0x03) << 4) + ((char_array_3[2] & 0xf0) >> 4);
char_array_4[3] = (char_array_3[2] & 0xfc) >> 2;
if (isnan(char_array_4[1])) {
char_array_4[2] = char_array_4[1] = 64;
} else if (isnan(char_array_4[2])) {
char_array_4[3] = 64;
}
for (j = 0; (j < i + 1); j++)
ret += base64_chars[char_array_4[j]];
while((i++ < 3))
ret += '=';
}
return ret;
}
JS代码:
var Base64 = {
_keyStr: ".ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+=",
encode : function (input) {
var output = [],
chr1, chr2, chr3, enc1, enc2, enc3, enc4,
i = 0;
while (i < input.length) {
chr1 = input[i++];
chr2 = input[i++];
chr3 = input[i++];
enc1 = chr1 & 0x3f;
enc2 = (chr1 >> 6) | ((chr2 & 0xf) << 2);
enc3 = (chr2 >> 4) | ((chr3 & 0x3) << 4);
enc4 = chr3 >> 2;
if (isNaN(chr2)) {
enc3 = enc4 = 64;
} else if (isNaN(chr3)) {
enc4 = 64;
}
output.push([this._keyStr.charAt(enc1),
this._keyStr.charAt(enc2),
this._keyStr.charAt(enc3),
this._keyStr.charAt(enc4)].join(''));
}
return output.join('');
},
decodeAsArray: function (b) {
var d = this.decode(b),
a = [],
c;
//alert("decoded base64:" + d);
for (c = 0; c < d.length; c++) {
a[c] = d.charCodeAt(c)
}
//alert("returning a");
return a
},
decode: function( input ) {
var output = "";
var chr1, chr2, chr3 = "";
var enc1, enc2, enc3, enc4 = "";
var i = 0;
do {
enc1 = this._keyStr.indexOf(input.charAt(i++)) ;
enc2 = this._keyStr.indexOf(input.charAt(i++)) ;
enc3 = this._keyStr.indexOf(input.charAt(i++)) ;
enc4 = this._keyStr.indexOf(input.charAt(i++)) ;
chr1 = (enc1 | ((enc2 & 3) << 6));
chr2 = (enc2 >> 2) | ((enc3 & 0x0F) << 4);
chr3 = (enc3 >> 4) | (enc4 << 2);
output = output + String.fromCharCode(chr1);
if (enc3 != 64) {
output = output + String.fromCharCode(chr2);
}
if (enc4 != 64) {
output = output + String.fromCharCode(chr3);
}
chr1 = chr2 = chr3 = "";
enc1 = enc2 = enc3 = enc4 = "";
} while (i < input.length);
return (output);
}
};
最佳答案
因此,当将您的 C++ 代码与 JavaScript 进行比较时,isnan() 应如下所示:
if (isnan(char_array_3[1])) { // char_array_3[1] = chr2
char_array_4[2] = char_array_4[1] = 64; // char_array_4[2] = enc3 & char_array_4[1] = enc2
} else if (isnan(char_array_3[2])) { // char_array_3[2] = chr3
char_array_4[3] = 64; // char_array_4[3] = enc2
}
But the main problem is that the
isnan()
function is only dedicated to floating-point value in C++ and doesn't have the same meaning as in JavaScript.
而不是使用 isnan()
功能,替换base64_encode()
的以下部分:
while (in_len--) {
char_array_3[i++] = *(bytes_to_encode++);
if (i == 3) {
...
if (isnan(char_array_4[1])) {
char_array_4[2] = char_array_4[1] = 64;
} else if (isnan(char_array_4[2])) {
char_array_4[3] = 64;
}
...
for(i = 0; (i < 4) ; i++)
ret += base64_chars[char_array_4[i]];
i = 0;
}
由以下一个:
1- to prevent unexpected value when less than 3 bytes left in the input buffer, force them to 0x00. Also before every next loop (
for(j=0;j<3;j++) char_array_3[j]=0x00;
).2- when 2 bytes have been loaded from the input buffer
if (i == 2)
, the last item of the output buffer is set to 64.3- when only 1 byte has been loaded from the input buffer
if (i == 1)
, the 2 last items of output buffer are set to 64.
for(j=0;j<3;j++) char_array_3[j]=0x00; // initialize input array
while (in_len--) {
char_array_3[i++] = *(bytes_to_encode++);
if ((i == 3) || (in_len == 0)) { // encode when 3 bytes or end of buffer
...
if (i == 1) { // instead of (isnan(char_array_4[1]))
// both char_array_3[1] and char_array_3[2] are not defined
char_array_4[3] = char_array_4[2] = 64;
} else if (i == 2) { // instead of (isnan(char_array_4[2]))
// char_array_3[2] is not defined
char_array_4[3] = 64;
}
...
for(i = 0; (i < 4) ; i++)
ret += base64_chars[char_array_4[i]];
i = 0;
for(j=0;j<3;j++) char_array_3[j]=0x00; // initialize input array
}
base64_encode()
中的最后一个错误与 JavaScript 相比,C++ 中的函数是在中间项的输出缓冲区计算中。
而不是以下作业:
char_array_4[0] = char_array_3[0] & 0x3f;
char_array_4[1] = ((char_array_3[0] & 0x0f) << 2) + ((char_array_3[1] & 0xc0) >> 6); // NOK
char_array_4[2] = ((char_array_3[1] & 0x03) << 4) + ((char_array_3[2] & 0xf0) >> 4); // NOK
char_array_4[3] = (char_array_3[2] & 0xfc) >> 2;
使用以下的:
1- When calculating
char_array_4[1]
(=enc2 in JS), the entrieschar_array_3[0]
(=chr1 in JS) andchar_array_3[1]
(=chr2 in JS) are reversed.2- When calculating
char_array_4[2]
(=enc3 in JS), the entrieschar_array_3[1]
(=chr2 in JS) andchar_array_3[2]
(=chr3 in JS) are reversed.
// JS => enc1 = chr1 & 0x3f;
char_array_4[0] = (char_array_3[0] & 0x3f); // OK
// JS => enc2 = (chr1 >> 6) | ((chr2 & 0xf) << 2);
char_array_4[1] = ((char_array_3[0] & 0xc0) >> 6) + ((char_array_3[1] & 0x0f) << 2); // OK
// JS => enc3 = (chr2 >> 4) | ((chr3 & 0x3) << 4);
char_array_4[2] = ((char_array_3[1] & 0xf0) >> 4) + ((char_array_3[2] & 0x03) << 4); // OK
// JS => enc4 = chr3 >> 2;
char_array_4[3] = (char_array_3[2] & 0xfc) >> 2;
After those corrections, the conditional block
if (i)
is useless and shall be removed.
关于javascript - C++中Base64编码函数的位移位,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/40318378/