Converting from Platform::String^ to std::string corrupts the string?

Question

I am building a windows phone app and i added a windows phone runtime component with this function in order to decode a string which i provide. The same function seems to be working correctly in a console application if i provide an std::string and return the same type. I think my problem is that i am converting from one type to another in the wrong way, but i can't see what i am doing wrong!

String^ Base64Encoding::base64_decode(String^ someString) {
    std::wstring ws1(someString->Data());
    std::string encoded_string(ws1.begin(), ws1.end());

    int in_len = encoded_string.size();
    int i = 0;
    int j = 0;
    int in_ = 0;
    unsigned char char_array_4[4], char_array_3[3];
    std::string ret;

    while (in_len-- && (encoded_string[in_] != '=') && is_base64(encoded_string[in_])) {
        char_array_4[i++] = encoded_string[in_]; in_++;
        if (i == 4) {
            for (i = 0; i <4; i++)
                char_array_4[i] = base64_chars.find(char_array_4[i]);

            char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
            char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
            char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];

            for (i = 0; (i < 3); i++)
                ret += char_array_3[i];
            i = 0;
        }
    }   
    if (i) {
        for (j = i; j <4; j++)
            char_array_4[j] = 0;

        for (j = 0; j <4; j++)
            char_array_4[j] = base64_chars.find(char_array_4[j]);

        char_array_3[0] = (char_array_4[0] << 2) + ((char_array_4[1] & 0x30) >> 4);
        char_array_3[1] = ((char_array_4[1] & 0xf) << 4) + ((char_array_4[2] & 0x3c) >> 2);
        char_array_3[2] = ((char_array_4[2] & 0x3) << 6) + char_array_4[3];

        for (j = 0; (j < i - 1); j++) ret += char_array_3[j];

    }
    std::wstring widestr = std::wstring(ret.begin(), ret.end());
    const wchar_t* wcstring2 = widestr.c_str();
    return ref new String(wcstring2);

}

So what am i doing wrong here?

Answer 1

Normally, the output of a Base64 decode isn't a string, it's a byte array. Base64 can encode arbitrary binary data, and depending on the string's encoding, not all byte arrays are valid strings.

To do a Base64 decode, use Convert::FromBase64String. If you want to interpret that byte array as a string, I suggest you use one of the Encoding classes, such as Encoding.Unicode, to do that conversion.