How to Safely Convert a String to an Integer in C ?

Convert String to Int with Bool/Fail in C

Introduction:

In C , converting a string to an integer can be a straightforward task, but there are cases where we may encounter conversion failures. In such scenarios, it becomes necessary to handle these exceptions or failures gracefully.

Boost::lexical_cast:

Boost provides a versatile library with numerous utilities, including boost::lexical_cast. This function allows for the conversion of strings to various data types and throws an exception in case of failure. For instance:

<code class="cpp">#include <boost/lexical_cast.hpp>
int i = boost::lexical_cast<int>(s);</code>

Without Boost:

If Boost is not available, we can utilize a C stream-based approach:

<code class="cpp">#include <sstream>
int i;
std::stringstream ss(s);
if ((ss >> i).fail() || !(ss >> std::ws).eof()) {
  throw std::bad_cast();
}</code>

Faking Boost:

In the absence of Boost, it is possible to create a custom function that mimics its functionality:

<code class="cpp">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;
}</code>

No-Throw Versions:

If desired, non-throw versions of these functions can be created by catching the appropriate exceptions and returning a boolean indicating success or failure:

<code class="cpp">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;
  }
}</code>

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