Thread: Best way to return a const char* from a string

I am trying to overload the what() method of the exception class which returns a const char*.

What's the best way to do it if I have a std::string on the stack, storing the string I want to return?

Obviously

Code:

return mystr.c_str();

is not a good idea because mystr would be deallocated by the time the caller reads the string.

Allocating a buffer of the same size on the stack and copying the string to it will work, but isn't that leaky? ("delete[] e.what();" just looks... wrong to me)

What's the conventional way to go about doing this?

Just keep an internal copy of the string:

Code:

class my_exception : public std::exception
{
	my_exception( string const& message )
	: message( message )
	{	}
	
	virtual char const* what( void ) const throw( )
	{
		return message.c_str( );
	}
	
	virtual ~my_exception( void ) throw( )
	{	}
	
	string
		message;	
};

Ah thanks.

But that means the string will live only as long as the exception object? So if I have, say

Code:

const char *error_msg;
try {
     //something
} catch (my_exception &e) {
     error_msg = e.what();
}
//do something with error_msg

Does it work? When does the exception object die?

The exception goes out of scope after the catch block, so you'd need something like:

Code:

string error_msg;
try {
     //something
} catch (my_exception &e) {
     error_msg = e.what();
}
//do something with error_msg

I see.

Thanks for your help!