C++ converting long hex string to binary

Question

I found similar solution here: Missing punctuation from C++ hex2bin and use that answer:

std::string hex2bin(std::string const& s) {

    std::string sOut;
    sOut.reserve(s.length()/2);

    std::string extract;
    for (std::string::const_iterator pos = s.begin(); pos<s.end(); pos += 2)
    {
        extract.assign(pos, pos+2);
        sOut.push_back(std::stoi(extract, nullptr, 16));
    }
    return sOut;
}

int main()
{
    printf("DECODED: %s\n", hex2bin("5468697320697320612031323320746573742e").c_str());

}

thats print like in example:

DECODED: This is a 123 test.

but it seems not working well for longer hex strings, for example:

printf("DECODED: %s\n", hex2bin("0200000081cd02ab7e569e8bcd9317e2fe99f2de44d49ab2b8851ba4a308000000000000e320b6c2fffc8d750423db8b1eb942ae710e951ed797f7affc8892b0f1fc122bc7f5d74df2b9441a42a14695").c_str());

and result is:

DECODED:

so how can it be done with C++.

I'm more familiar with php and there is function hex2bin that do all the job.

Little update about that: I was using that function:

std::string hex2bin(std::string s) {
    std::string rc;
    int nLen = s.length();
    int tmp;
    for (int i(0); i + 1 < nLen; i += 2) {
        if (std::istringstream(s.substr(i, 2)) >> std::hex >> tmp) {
            rc.push_back(tmp);
        }
    }
    return rc;
}

and what thats function returns char by char: C++

index 0: 2
index 1: 0
index 2: 0
index 3: 0
index 4: -127
index 5: -51
index 6: 2
index 7: -85
index 8: 126
index 9: 86
index 10: -98
index 11: -117
index 12: -51
index 13: -109
index 14: 23
index 15: -30
index 16: -2
index 17: -103
index 18: -14
index 19: -34
index 20: 68
index 21: -44
index 22: -102
index 23: -78
index 24: -72
index 25: -123
index 26: 27
index 27: -92
index 28: -93
index 29: 8
index 30: 0
index 31: 0
index 32: 0
index 33: 0
index 34: 0
index 35: 0
index 36: -29
index 37: 32
index 38: -74
index 39: -62
index 40: -1
index 41: -4
index 42: -115
index 43: 117
index 44: 4
index 45: 35
index 46: -37
index 47: -117
index 48: 30
index 49: -71
index 50: 66
index 51: -82
index 52: 113
index 53: 14
index 54: -107
index 55: 30
index 56: -41
index 57: -105
index 58: -9
index 59: -81
index 60: -4
index 61: -120
index 62: -110
index 63: -80
index 64: -15
index 65: -4
index 66: 18
index 67: 43
index 68: -57
index 69: -11
index 70: -41
index 71: 77
index 72: -14
index 73: -71
index 74: 68
index 75: 26
index 76: 66
index 77: -95
index 78: 70
index 79: -107

PHP

index 0: 2
index 1: 0
index 2: 0
index 3: 0
index 4: 129
index 5: 205
index 6: 2
index 7: 171
index 8: 126
index 9: 86
index 10: 158
index 11: 139
index 12: 205
index 13: 147
index 14: 23
index 15: 226
index 16: 254
index 17: 153
index 18: 242
index 19: 222
index 20: 68
index 21: 212
index 22: 154
index 23: 178
index 24: 184
index 25: 133
index 26: 27
index 27: 164
index 28: 163
index 29: 8
index 30: 0
index 31: 0
index 32: 0
index 33: 0
index 34: 0
index 35: 0
index 36: 227
index 37: 32
index 38: 182
index 39: 194
index 40: 255
index 41: 252
index 42: 141
index 43: 117
index 44: 4
index 45: 35
index 46: 219
index 47: 139
index 48: 30
index 49: 185
index 50: 66
index 51: 174
index 52: 113
index 53: 14
index 54: 149
index 55: 30
index 56: 215
index 57: 151
index 58: 247
index 59: 175
index 60: 252
index 61: 136
index 62: 146
index 63: 176
index 64: 241
index 65: 252
index 66: 18
index 67: 43
index 68: 199
index 69: 245
index 70: 215
index 71: 77
index 72: 242
index 73: 185
index 74: 68
index 75: 26
index 76: 66
index 77: 161
index 78: 70
index 79: 149

so as You can notice values that are in C++ less then 0 are displayed in php in another what. I would like to have same functionality link in php.

Answer 1

您的示例包含数字“00”，它将转换为字符值0，printf将其解释为零终止符并停止打印。

Answer 2

 printf("DECODED: %s\\n", hex2bin("0200000081cd02ab7e569e8bcd9317e2fe99f2de44d49ab2b8851ba4a308000000000000e320b6c2fffc8d750423db8b1eb942ae710e951ed797f7affc8892b0f1fc122bc7f5d74df2b9441a42a14695").c_str()); 

The hex2bin function actually returns a std::string with 80 characters. It's just a display problem. Just print the characters along with their integer values individually to see the problem:

std::string const s = hex2bin("0200000081cd02ab7e569e8bcd9317e2fe99f2de44d49ab2b8851ba4a308000000000000e320b6c2fffc8d750423db8b1eb942ae710e951ed797f7affc8892b0f1fc122bc7f5d74df2b9441a42a14695");

for (std::string::size_type i = 0; i < s.size(); ++i)
{
    std::cout << "index " << i << ": " << static_cast<int>(s[i]) << ", printed like this: " << s[i] << "\n";
}

You will get output like this:

index 0: 2, printed like this: ☻
index 1: 0, printed like this:
index 2: 0, printed like this:

[...]

index 77: -95, printed like this: í
index 78: 70, printed like this: F
index 79: -107, printed like this: ò

---

In my opinion, a function like hex2bin should return std::vector<char> because it conveys the intent better, and it is harder to print incorrectly. Binary data should not be fed to std::cout or printf as if it was a human-readable string, without the compiler having any chance to complain.