How to Convert Strings to Hexadecimal and Back in C ?

Converting Strings to Hex and Back in C

Manipulating strings and hexadecimal numbers is a common task in programming. In C , the standard library provides a set of functions for these operations.

String to Hex (string_to_hex)

Converting a string to hexadecimal is achieved using the string_to_hex function. The function iterates through each character in the input string, extracts its hexadecimal value, and appends it to the output string. For example, the string "Hello World" would be converted to "48656C6C6F20576F726C64".

std::string string_to_hex(const std::string& input)
{
    static const char hex_digits[] = "0123456789ABCDEF";

    std::string output;
    output.reserve(input.length() * 2);
    for (unsigned char c : input)
    {
        output.push_back(hex_digits[c >> 4]);
        output.push_back(hex_digits[c & 15]);
    }
    return output;
}

Hex to String (hex_to_string)

To convert a hexadecimal string back to a regular string, use the hex_to_string function. Here, each pair of hexadecimal digits is converted to an integer, and the resulting integers are concatenated to form the output string.

std::string hex_to_string(const std::string& input)
{
    const auto len = input.length();
    if (len & 1) throw std::invalid_argument("odd length");

    std::string output;
    output.reserve(len / 2);
    for (auto it = input.begin(); it != input.end(); )
    {
        int hi = hex_value(*it++);
        int lo = hex_value(*it++);
        output.push_back(hi << 4 | lo);
    }
    return output;
}

This allows you to effortlessly convert between string and hexadecimal data in C , making it convenient for various programming scenarios.

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