how to convert a set of hex strings to byte array

Question

I have an input of char *str = "13 00 0A 1B CA 00";

I need an output as BYTE bytes[] = { 0x13, 0x00, 0x0A, 0x1B, 0xCA, 0x00 };

can somebody help with a solution?

`sscanf` might work, but he may not know the exact number of bytes in the string, so he needs a more dynamic approach. — sean, Dec 21 '12 at 16:08
sscanf is not safe, it causes 'buffer overrun'. http://stackoverflow.com/questions/5873402/is-sscanf-considered-safe-to-use — alex, Dec 21 '12 at 16:21

sean · Accepted Answer · 2012-12-21T16:32:49.537

7

You will need to parse out each of the two characters and then convert them into BYTE. This isn't fairly difficult to do.

std::stringstream converter;
std::istringstream ss( "13 00 0A 1B CA 00" );
std::vector<BYTE> bytes;

std::string word;
while( ss >> word )
{
    BYTE temp;
    converter << std::hex << word;
    converter >> temp;
    bytes.push_back( temp );
}

edited Dec 21 '12 at 16:32

answered Dec 21 '12 at 16:06

sean

3,955
21
28

Which c++ compiler are you using that has a function named hex_string_to_int in the standard library? – EvilTeach Dec 21 '12 at 16:09
I'm sorry that is not exactly what I ment, I'm going to change that. – sean Dec 21 '12 at 16:10
I didn't quite understand this, can you explain in more detail please> – Dean Dec 21 '12 at 16:14
my strings are "xx xx xx xx" format, will strstream work with the spaces? – Dean Dec 21 '12 at 16:15
typedef unsigned short BYTE; – evpo Nov 03 '13 at 07:31
why extra stream `converter` is used? It can be done directly on the `ss` stream! – Marek R Feb 22 '16 at 07:45

Itsik · Answer 2 · 2012-12-21T16:23:47.177

This answer assumes that the input format is actually 3 chars for each hex BYTE. I used sscanf for simplicity, streams are obviously also an option.

    std::vector<BYTE> bytes;
    char *str = "13 00 0A 1B CA 00";
    std::string input(str);

    size_t count = input.size()/3;
    for (size_t i=0; i < count; i++)
    {           
        std::string numStr = input.substr(i*3, input.find(" "));

        int num=0;
        sscanf(numStr.c_str(), "%x", &num);
        bytes.push_back((BYTE)num);
    }

    // You can access the output as a contiguous array at &bytes[0]
    // or just add the bytes into a pre-allocated buffer you don't want vector

Actually `count` of bytes is `(input.size() + 1)/3`. Your code will miss last byte in input string. — renadeen, Dec 02 '13 at 14:38

how to convert a set of hex strings to byte array

2 Answers2