Thread: What happens with returned pointer

Hi everybody.

Question is about pointers returned from functions.

There is function

Code:

char *PQescapeLiteral(PGconn *conn, const char *str, size_t length);

that returns escaped version of passed str parameter.


What happens with this pointer and memory allocated in case I use it in some way like this:

Code:

printf("SELECT * FROM lala WHERE lolo = '%s'", 
PQescapeLiteral(DBConnection, "'''ddsa", 3))

I mean if this pointer and allocated memory for it hang till the end of program, or it's automatically freed after printf?


Thanks in advance.

Laserlight,
Thanks for your response.
Now it's clear.

Originally Posted by datswd

I mean if this pointer and allocated memory for it hang till the end of program, or it's automatically freed after printf?

C has no way of automatically freeing things. It's not like in C++ where you have smart pointers that free themselves when they go out of scope or a garbage collected language like C# or Java where things get automatically freed periodically if nothing references them. C has none of that at all. You must always, always read the manual or source code for functions you're working with that return pointers so you know what to do with the pointer when you're finished. One of two things generally happen when something returns a char*, it either allocated something that you're expected to malloc or it returned a pointer to a static array or some other value that you're not expected to free. There's no way to tell just from the function prototype which one it is, you must always, always read the manual or source code carefully to know what to do with it.

Things are freed, however, at the end of the program as you implied. The OS knows what memory you allocated and will clean it up. For short programs that don't allocate large amounts of memory it's common to see no free calls at all. It's probably not the best practice, but there's no sense in wasting your time freeing something if you're just ending the program anyway. So if you're looking at code that uses this function and they don't free it, they're either making a mistake, or leaving it to the OS.