How to Convert a C Hex String to a Signed Integer?

C Hex String to Signed Integer Conversion

Suppose you have a hexadecimal string and wish to convert it to a signed 32-bit integer in C . For instance, given the hex string "fffefffe," the binary representation is 11111111111111101111111111111110. This represents a signed integer of -65538.

Conversion Procedure:

To conduct this conversion effectively, utilize std::stringstream as follows:

unsigned int x;
std::stringstream ss;
ss << std::hex << "fffefffe";
ss >> x;

For example, the following code snippet yields -65538:

#include <sstream>
#include <iostream>

int main() {
    unsigned int x;
    std::stringstream ss;
    ss << std::hex << "fffefffe";
    ss >> x;
    // Output as a signed type
    std::cout << static_cast<int>(x) << std::endl;
}

C 11 String Conversion Functions:

For C 11 or later, the new string to number utilities simplify this process. The "stol" (string to long) and "stoul" (string to unsigned long) functions provide thin wrappers around C's string conversion capabilities.

std::string s = "0xfffefffe";
unsigned int x = std::stoul(s, nullptr, 16);

Additional Considerations:

Note that Boost also provides helpful functionality for this conversion, including error checking capabilities.

However, for simplicity and portability, it is recommended to use the built-in stringstream or C 11 utility functions presented here.

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