Questions about free() 1

mattias1975 · Oct 16, 2004

Hello!

Is there any rule when to use the function free()?
Some times when i use it i get the message
"Segmentation fault" from the compiler. Why?

Salem · Oct 16, 2004

> Is there any rule when to use the function free()?
You call it exactly ONCE for each result returned by malloc / calloc / realloc

> "Segmentation fault" from the compiler. Why?
It's not from the compiler, its from the operating system stopping your errant program from causing any more damage.

It usually means you messed up with the memory you got from malloc - example

Code:

char *p = malloc( 10 );     /* 9 chars and a \0 max */
strcpy( p, "hello world" ); /* this is too much!!! */

What happens next is anyone's guess.

At some random point in the future (perhaps never), there is a chance that any following call to malloc or free will crash in a manner you describe. The failure to crash of course does not mean that the program is bug free.

Of course the real trick is figuring out the cause (where the memory was corrupted) as opposed to the effect (where the problem was noticed in the form of a segfault).

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Questions about free() 1

mattias1975

Programmer

Salem

Programmer

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