User's Guide

Exception Handling as Defined by the ANSI/ISO C++ International Standard
The Standard C++ Library provides classes that C++ programs can use for reporting errors. These
classes are defined in the header file <stdexcept> and described in the ANSI/ISO C++
International Standard.
• The class, exception, is the base class for object types thrown by the Standard C++ Library
components and certain expressions.
• The class, runtime_error, defines errors due to events beyond the scope of the program.
• The class, logic_error, defines errors in the internal logic of the program.
Basic Exception Handling Example
The simple program shown here illustrates exception handling concepts. This program contains a
try block (from which a range error is thrown) and a catch clause, which prints the operand of the
throw.
This program also uses the runtime_error class defined in the Standard C++ Library to report
a range error.
#include <stdexcept>
#include <iostream.h>
#include <string>
void fx ()
{
// details omited
throw range_error(string(“some info”));
}
int main ( )
{
try {
fx ();
} catch (runtime_error& r) {
cout <<r.what() << ‘\n’;
}
}
Function Try Block Examples
A function can catch exceptions thrown during its execution by associating catch handlers with its
body, using a function try block. Note the difference between the following example and the
previous exception handling example. In this case, the try keyword comes before the function
body’s opening brace, and the catch handler comes after the function body’s closing brace.
#include <stdexcept>
#include <iostream.h>
#include <string>
void fx ()
{
// .......
throw range_error(string(“some info”));
}
int main ( )
try {
fx ();
}
catch (runtime_error& r) {
cout <<r.what() << ‘\n’; }
Function try blocks are sometimes necessary with class constructor destruction. A function try block
is the only means of ensuring that all exceptions thrown during the construction of an object are
caught within the constructor. For example,
162 Exception Handling