Checking for Leaks

If memory leak checking is turned on, a scan for memory leaks is automatically performed just before the program being tested exits. Any detected leaks are reported. The program should not be killed with the kill command. Here is a typical memory leak error message:

Memory leak (mel):
Found leaked block of size 6 at address 0x21718
At time of allocation, the call stack was:
    [1] foo() at line 63 in test.c
    [2] main() at line 47 in test.c

A UNIX program has a main procedure (called MAIN in f77) that is the top-level user function for the program. Normally, a program terminates either by calling exit(3) or by returning from main. In the latter case, all variables local to main go out of scope after the return, and any heap blocks they pointed to are reported as leaks (unless global variables point to those same blocks).

It is a common programming practice not to free heap blocks allocated to local variables in main, because the program is about to terminate and return from main without calling exit(). To prevent runtime checking from reporting such blocks as memory leaks, stop the program just before main returns by setting a breakpoint on the last executable source line in main. When the program halts there, use the showleaks command to report all the true leaks, omitting the leaks that would result merely from variables in main going out of scope.

For more information, see showleaks Command.