How to throw a C++ exception

Question

I have a very poor understanding of exception handling(i.e., how to customize throw, try, catch statements for my own purposes).

For example, I have defined a function as follows: int compare(int a, int b){...}

I'd like the function to throw an exception with some message when either a or b is negative.

How should I approach this in the definition of the function?

Answer 1

Simple:

#include <stdexcept>  int compare( int a, int b ) {     if ( a < 0 || b < 0 ) {         throw std::invalid_argument( "received negative value" );     } } 

The Standard Library comes with a nice collection of built-in exception objects you can throw. Keep in mind that you should always throw by value and catch by reference:

try {     compare( -1, 3 ); } catch( const std::invalid_argument& e ) {     // do stuff with exception...  } 

You can have multiple catch() statements after each try, so you can handle different exception types separately if you want.

You can also re-throw exceptions:

catch( const std::invalid_argument& e ) {     // do something      // let someone higher up the call stack handle it if they want     throw; } 

And to catch exceptions regardless of type:

catch( ... ) { };