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C strings and memory problems

Started by mike25025 Sep 11, 2005 at 6:46 PM 3 replies 950+ views

Original Post

Sep 11, 2005 at 6:46 PM

I have a function that is implemented in C++ like this (Not actual implementation. Just an example of what I'm tying to do.)

const char* getName()
{
	return obj->getName().c_str(); // g_obj->getName returns std::string
}

It is called from C so I cant return std::string. How can I return a C string without memory problems?

Koshmaar

Sep 11, 2005 at 6:52 PM

What memory problems are you reffering to? AFAIK, you can safely perform read-only operartions on returned in such a way string, and nothing will be leaked. Of course, if you want to write, you have to copy it - but that's logical, isn't it? :-)

mike25025

Sep 11, 2005 at 6:59 PM

obj->getName returns a std::string that is destroyed when the function returns. If I try to read from the C string the program crashes.

Enigma

Sep 11, 2005 at 7:03 PM

If you know that the calling C code will (or can be made to) free the string you return when it is no longer needed then just return strdup(blah.c_str()). Otherwise you'll have to redesign your code so that you return a c_str() of a std::string that has a longer lifetime, just like you'd have to if you weren't dealing with std::string objects at all and had to return a valid char const[].

Enigma

mike25025

Sep 11, 2005 at 7:06 PM

Quote:
Original post by Enigma
If you know that the calling C code will (or can be made to) free the string you return when it is no longer needed then just return strdup(blah.c_str()).

I think Ill do that. Thank you for your help.

[Edited by - mike25025 on September 11, 2005 7:06:21 PM]

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