Best way to return a const char* from a string

This is a discussion on Best way to return a const char* from a string within the C++ Programming forums, part of the General Programming Boards category; I am trying to overload the what() method of the exception class which returns a const char*. What's the best ...

  1. #1
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    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?

  2. #2
    Guest Sebastiani's Avatar
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    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;	
    };

  3. #3
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    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?

  4. #4
    Guest Sebastiani's Avatar
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    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

  5. #5
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    I see.

    Thanks for your help!

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