How to Convert Strings to Integers with Error Handling in C ?

Converting Strings to Integers with Error Handling in C

In programming, it's often necessary to convert strings to integers. While C provides the std::atoi function for this purpose, it doesn't handle conversion errors gracefully. To address this, we seek a solution that allows for error handling, similar to C#'s Int32.TryParse.

Boost's Lexical Cast Function

An efficient approach is to use the lexical_cast function from the Boost library. It supports a variety of data types and can throw an exception if the cast fails. Here's an example:

<code class="cpp">#include <boost/lexical_cast.hpp>

int main() {
    std::string s;
    std::cin >> s;

    try {
        int i = boost::lexical_cast<int>(s);

        // ...
    } catch (...) {
        // Handle error
    }
}</code>

Using Standard Library Functions

If Boost is not available, a combination of std::stringstream and >> operator can be used:

<code class="cpp">#include <iostream>
#include <sstream>
#include <string>

int main() {
    std::string s;
    std::cin >> s;

    try {
        std::stringstream ss(s);

        int i;
        if ((ss >> i).fail() || !(ss >> std::ws).eof()) {
            throw std::bad_cast();
        }

        // ...
    } catch (...) {
        // Handle error
    }
}</code>

Faking Boost's Lexical Cast

As a final alternative, a "fake" version of Boost's lexical_cast function can be created:

<code class="cpp">#include <iostream>
#include <sstream>
#include <string>

template <typename T>
T lexical_cast(const std::string& s) {
    std::stringstream ss(s);

    T result;
    if ((ss >> result).fail() || !(ss >> std::ws).eof()) {
        throw std::bad_cast();
    }

    return result;
}

int main() {
    std::string s;
    std::cin >> s;

    try {
        int i = lexical_cast<int>(s);

        // ...
    } catch (...) {
        // Handle error
    }
}</code>

No-throw Versions

If a no-throw version is desired, catch the appropriate exceptions and return a boolean indicating success or failure:

<code class="cpp">template <typename T>
bool lexical_cast(const std::string& s, T& t) {
    try {
        t = lexical_cast<T>(s);
        return true;
    } catch (const std::bad_cast& e) {
        return false;
    }
}

int main() {
    std::string s;
    std::cin >> s;

    int i;
    if (!lexical_cast(s, i)) {
        std::cout << "Bad cast." << std::endl;
    }
}</code>

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