使用C++解码base64/UTF-16LE

Question

我的问题是试图解码一个base64 / UTF-16LE字符串。此解码的结果始终是第一个字符。如果将字符串解码为utf-8 / ascii / windows1252，则结果是正确的。

有人能有现成的解决方案吗？

我使用的是来自互联网的标准代码：

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

int main()
{
    b64_decode_string("SABlAGwAbABvAA==");
    
    return 0;
}


char base64decode_lut[] = {
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 62, 64, 64, 64, 63,
    52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 64, 64, 64, 64, 64, 64,
    64,  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, 64, 64, 64, 64, 64,
    64, 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, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64,
    64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64
};
 

void base64decode(char *src, char *dest, int len)
{
    int i=0, slen=strlen(src);
    for(i=0;i<slen&&i<len;i+=4,src+=4)
    { 
        char c1=base64decode_lut[*src], c2=base64decode_lut[*(src+1)], c3=base64decode_lut[*(src+2)], c4=base64decode_lut[*(src+3)];

        *(dest++)=(c1&0x3F)<<0x2|(c2&0x30)>>0x4;
        *(dest++)=(c3!=64)?((c2&0xF)<<0x4|(c3&0x3C)>>0x2):'\0';
        *(dest++)=(c4!=64)?((c3&0x3)<<0x6|c4&0x3F):'\0';
    }
    *dest='\0'; // Append terminator
}
 
 
int b64_decode_string(char *source)
{
    int dest_size;
    int res;
    char *dest;

    dest_size = strlen(source);
    dest = (char *)malloc(dest_size);

    memset(dest,0,dest_size);
    base64decode(source, dest, dest_size);
    printf("Decode: %s", dest);
}

Answer 1

只对第一个字符进行解码的原因是因为第二个字符以0x00字节开始，所以调用strlen() (仅适用于ascii字符串)返回一个非常小的数字(如1或2)，而不是字符串的实际长度。

建议熟悉宽类型和处理宽字符的函数，比如：wprintf()和字符串的‘wchar_t’修饰符：-L和头文件：wchar.h

how to handle wide character strings

Answer 2

这里没有使用C字符串，因此不要使用诸如strlen();之类的字符串函数

并考虑使用unsigned char作为数组的类型

unsigned char base64decode{} = {...

在这种情况下，数组元素的数量可以由以下语句确定：

size_t len = sizeof(base64decode_lut)/sizeof(base64decode_lut[0]);