Doubt about freeing memory

Hello. I'm using this function to concatenate two strings, and return the resulting string.

Code:

---

char * concatenate (char* str1, char* str2)
{
        char *result;
        if ( str2 != NULL )
        {
                result = malloc(strlen(str1) + strlen(str2) + 1);
                if ( result != NULL )
                {
                        strcpy(result, str1);
                        strcat(result, str2);
                }
        }
        return result;
}

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My question, Is this function leaking memory?
If it does, is there another way to do it? I just ran out of ideas.

Thanks!!!

That function in itself doesn't leak memory, but if you don't eventually free the pointer that came back from the function, then you are leaking.

[And in English you don't say "Doubt about ...", but "Question about ..."]

--
Mats

Thanks a lot. That's what I thought.

"I Doubt..." means "I don't believe..." which is a statement, not a question.

Quote:

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Originally Posted by cpjust

"I Doubt..." means "I don't believe..." which is a statement, not a question.

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Not necessarily.

"I am in doubt about how I would go about.. " is a perfectly valid sentence.

Quote:

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Originally Posted by cpjust

"I Doubt..." means "I don't believe..." which is a statement, not a question.

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No doubt!

I've a question about matsp's remark... HE states that the pointer returned from concatenate() will be left on the stack. Should main, therefore, be coded such as:

Code:

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int main(void)
  char * newstring ;
  newstring = concatenate("Hello ", "World") ;
  printf("%s\b",newstring) ;
  free(newstring) ;
}

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??

More thoughts - that would free the new malloc'ed storage - but what about freeing the returned pointer?

Quote:

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Originally Posted by Todd Burch

More thoghts - that would free the new malloc'ed storage - but what about freeing the returned pointer?

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That's exactly what you should free. Obviously, if you do something like this:

Code:

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char *a, *b, *c;
a = malloc(10);
strcpy(a, "Something");
b = malloc(10);
strcpy(b, "Otherstr");
c = concatenate(a, b);
...
free(c);

---

would leave a and b allocated but not freed.

Every malloc should have a matching free somewhere in the code - the number of malloc() and free() occurrences in the source code doesn't have to match, but the calls for malloc() should have a matching call to free() somewhere.

--
Mats

FWIW, a pointer to pointer might help you keep track of freeing memory where it is allocated, even if you previously allocated something.

Code:

---

#include <stdlib.h>
#include <string.h>
#include <stddef.h> /** for NULL and size_t **/

/** Concatenate string a to string b and store the result **/
char * concat ( char ** result, const char * a, const char * b )
{
    char * more = NULL;
    if ( a && b )
    {
        size_t alen = strlen( a );
        size_t blen = strlen( b );

        more = realloc( *result, alen + blen + 1 );
        if ( more )
        {
            strcpy( more, a );
            strcat( more, b );
            *result = more;
        }
    }
    return more;
}

int main ( void )
{
    char * p = NULL;
 
    if ( concat( &p, "Hello, ", "world." ) )
    {
        puts( p );
        free( p );
    }
    return 0;
}

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Quote:

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Originally Posted by matsp

[And in English you don't say "Doubt about ...", but "Question about ..."]

--
Mats

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Doubt is synonym of uncertainty.
If it is grammatically correct to say: Uncertainty about freeing memory, as a tittle, it is correct to write doubt about freeing memory, even when most people confuse doubt with question.