(C++) catch

catch is a keyword to mark a catch-block. A catch-block is always preceded by a try-block in which an exception might be thrown. The exception can be caught by the subsequent catch-block.

Example: std::stoi

std::stoi converts a std::string to integer

std::stoi example: input can be converted to integer

#include <cassert>
#include <string>

int main()
{
  assert(std::stoi("123") == 123);
}

std::stoi example: input is no integer

If the input cannot be converted to integer, a std::invalid_argument is thrown.

#include <cassert>
#include <stdexcept>
#include <string>

int main()
{
  try
  {
    std::stoi("this is no int");
    assert(!"Should not get here");
  }
  catch (const std::invalid_argument&)
  {
    assert("OK");
  }
}

std::stoi example: input is a too big integer

If the input is a too big integer, a std::out_of_range is thrown.

#include <cassert>
#include <stdexcept>
#include <string>

int main()
{
  try
  {
    std::stoi("12345678901234567890123456789012345678901234567890");
    assert(!"Should not get here");
  }
  catch (const std::out_of_range&)
  {
    assert("OK");
  }
}

std::stoi example: handle both exceptions

#include <cassert>
#include <stdexcept>
#include <string>

int main()
{
  try
  {
    std::stoi("[your string here]");
    assert(!"Should not get here");
  }
  catch (const std::invalid_argument&)
  {
    assert("OK");
  }
  catch (const std::out_of_range&)
  {
    assert("OK");
  }
}

As an alternative, the base of both exceptions (called std::exception) can be used:

#include <cassert>
#include <stdexcept>
#include <string>

int main()
{
  try
  {
    std::stoi("[your string here]");
    assert(!"Should not get here");
  }
  catch (const std::exception&)
  {
    assert("OK");
  }
}

Advice

• Don't try to catch every exception in every function [1]
• Always catch by reference[3], for example const std::invalid_argument&
• Have main catch and report every exception [2]

Reference

• [1] Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 13.7. Advice. page 387: '[8] 'Don't try to catch every exception in every function'
• [2] Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 13.7. Advice. page 387: '[27] 'Have main() catch and report every exception'
• [3] Bjarne Stroustrup. The C++ Programming Language (4th edition). 2013. ISBN: 978-0-321-56384-2. Chapter 30.5. Advice. page 883: '[10] Always catch exception& (for standard-library and language support exceptions) and ... (for unexpected exceptions)'