How to Efficiently Convert Between Hexadecimal Strings and Standard Strings in C ?

Converting Hexadecimal Strings to Strings in C

String conversion between hexadecimal and standard text formats requires a robust approach in C . Here's a detailed guide:

Convert String to Hexadecimal:

The string_to_hex() function offers a simple solution:

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;
}

Convert Hexadecimal to String:

For converting from hexadecimal to string, the hex_to_string() function ensures accuracy:

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;
}

Example Usage:

To demonstrate the functionality:

std::string original_string = "Hello World";
std::string hex_string = string_to_hex(original_string);
std::cout << "Hexadecimal representation: " << hex_string << std::endl;
std::string recovered_string = hex_to_string(hex_string);
std::cout << "Recovered string: " << recovered_string << std::endl;

Output:

Hexadecimal representation: 48656c6c6f20576f726c64
Recovered string: Hello World

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