Thread: exit()

According to the C standard:

Originally Posted by C Standard, 1999 Edition, Section 7.20.4.3

Code:

#include <stdlib.h>
void exit(int status);

The exit function causes normal program termination to occur. If more than one call to the exit function is executed by a program, the behavior is undefined.

First, all functions registered by the atexit function are called, in the reverse order of their registration, except that a function is called after any previously registered functions that had already been called at the time it was registered. If, during the call to any such function, a call to the longjmp function is made that would terminate the call to the registered function, the behavior is undefined.

Next, all open streams with unwritten buffered data are flushed, all open streams are closed, and all files created by the tmpfile function are removed.

Finally, control is returned to the host environment. If the value of status is zero or EXIT_SUCCESS, an implementation-defined form of the status successful termination is returned. If the value of status is EXIT_FAILURE, an implementation-defined form of the status unsuccessful termination is returned. Otherwise the status returned is implementation-defined.

Originally Posted by msshapira

Does it release allocations or not?

No, at least not according to the standard's description.

Originally Posted by msshapira

is there a function that can release all allocation (in case of allocation failure) without releasing alloc by alloc?

Generally, the operating system would do that for you anyway. It is not good practice to rely on that (and not all operating systems clean up after processes in that way), so you should still keep track of what you allocate and free the memory as soon as it is not needed.

Do you have any examples of which OS's don't clean up memory after a program ends?

Originally Posted by cpjust

Do you have any examples of which OS's don't clean up memory after a program ends?

I was thinking the same thing.

All OS's I've ever worked with that allow tasks/processes to end (without issuing some sort of "panic"), does clean up the memory allocated. I'm sure there are micro-OS's that have "no memory cleanup", but I also expect those do not use "exit" to end a process.

I'm not by any means saying you shouldn't make a best effort of cleaning up memory allocations in the code - for long-running applications, it will not work to "stick you head in the sand and hope for the best", as any memory leaks will accumulate and eventually cause the system to fall over.

For simple, short-running, applications, it is possibly permissable to explicitly NOT free memory.

Note that the freeing of memory in the relevant cases is done by the OS, not by the C runtime library. And it is done at a much coarser level than the C runtime library.

Also note that where I work, we make OS's for Mobile Phones, and we have specific testing to ensure that an application NEVER leaks memory - yes, it gets cleaned up if the app exits. The issue however, is that in embedded systems, there may not be a whole lot of free memory, and even a small amount of leaked memory from time to time can cause undesirable "failure to do the expected operation".

--
Mats