How to Convert Hex Strings to Signed Integers in C ?

Converting Hex Strings to Signed Integers in C

Consider the task of converting a hex string representation of a number to a 32-bit signed integer. For instance, the hex string "fffefffe" translates to 11111111111111101111111111111110 in binary, representing the signed integer -65538. Additionally, we need to handle both positive and negative numbers, such as "0000000A" (binary: 00000000000000000000000000001010; decimal: 10).

Solution: Utilizing std::stringstream

Leveraging the std::stringstream class, the conversion process becomes straightforward:

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

By extracting the integer from the stream, we obtain the 32-bit signed integer representation of the hex string.

Alternative Approaches

Boost's lexical_cast: Handling Errors (Discontinued)

Note: As indicated in the source answer, Boost's lexical_cast approach has been discontinued in favor of the newer C 11 functions.

Boost also provides a convenient solution that incorporates error checking:

try {
    unsigned int x = lexical_cast<int>("0x0badc0de");
} catch(bad_lexical_cast &amp;) {
    // Handle conversion error
}

Custom lexical_cast: Simple Implementation Without Error Checking

For those not utilizing Boost, a simplified version of lexical_cast can be employed without error handling:

template<typename T2, typename T1>
inline T2 lexical_cast(const T1 &amp;in) {
    T2 out;
    std::stringstream ss;
    ss << in;
    ss >> out;
    return out;
}

unsigned int x = lexical_cast<unsigned int>("0xdeadbeef");

Conclusion

Employing either std::stringstream or the newer C 11 utilities (such as std::stol), developers can efficiently convert hex strings to signed integers in C .

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