Re: Returning (char *) from a function - memory problem

From:

=?ISO-8859-1?Q?Erik_Wikstr=F6m?= <Erik-wikstrom@telia.com>

Newsgroups:

comp.lang.c++

Date:

Mon, 27 Aug 2007 16:22:47 GMT

Message-ID:

<rTCAi.7054$ZA.3565@newsb.telia.net>

On 2007-08-27 16:46, Jason wrote:

I don't know if anyone caught my previous post about a project I've
inherited, but I have another question about it.

(Quick summary:
I have old C code, converting to C++. Compiles and runs fine)

My problem is when the application exits, CodeGuard tells me that I have
memory leaks, and points to a function.

char *fooFunc(int Bar)
{
    char *returnArr = new char[8];
    int stuff;

    // do some stuff with Bar

    sprintf(returnArr,"%2d",stuff);
    return(returnArr);
}

I see that I am allocating memory, but it's not being freed. The function
is called like so:

fprintf(filePtr,"%s and stuff",fooFunc(myInt));

How do I free (delete) the memory allocated by this? I know I could change
it to

char returnArr[8];

but that would prevent me from learning anything new today.

I think these kinds of situation are handled in two different ways in C
libraries, the first is to use a static string (char array) in the
function and the result is then not thread safe (as Victor explained).
You could make it thread safe by using a string in TLS in a
multithreaded program, but it's not a good solution to begin with.

Another way is to change the method so that it takes a char* as argument
and performs the operations into this string, just like sprintf does.
This requires you to change the way you use the function, but you could
then use local variables like this

   char str[8];
   fooFunct(myInt, str;
   fprintf(filePtr,"%s and stuff",str);

--
Erik Wikstr?m