Only the handler whose argument type matches the type of the exception specified in the throw statement is executed. Multiple handlers (i.e., catch expressions) can be chained each one with a different parameter type. The catch block is skipped entirely and the program continues execution after the try-catch structure. If at least one argument is specified after the program name when the program is run, then no exception is thrown and the argument's value is printed. An error message is printed and then the program continues execution after the try-catch structure, not after the throw statement that threw the exception. In the example above, if no command line arguments are specified, the exception is thrown and program control is transferred to the catch handler block that matches the data type invalid_argument.
The type of this parameter is very important, since the type of the argument passed by the throw expression is checked against it, and only in the case that they match is the exception caught by that handler. The syntax for catch is similar to a regular function with one parameter. The exception handler is declared with the catch keyword immediately after the closing brace of the try block. The constructor for the class takes a string argument, which can later be accessed by calling the what() member function of the exception object passed to the exception handler. Invalid_argument is a standard library exception class defined in the header file stdexcept. A throw expression accepts an expression (in this case, an unnamed object of the class invalid_argument), which is passed as an argument to the exception handler. In this example this code simply throws an exception if there are no command-line arguments specified when the program is run. The code under exception inspection is enclosed in a try block.
Throw invalid_argument("No command line arguments specified")
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