#### 3.2.4.3 Some more or less clever ideas ¶

You know the situation. The program is prepared for debugging and in all debugging sessions it runs well. But once it is started without debugging the error shows up. A typical example is a memory leak that becomes visible only when we turn off the debugging. If you foresee such situations you can still win. Simply use something equivalent to the following little program:

    #include <mcheck.h>
    #include <signal.h>

    static void
    enable (int sig)
    {
      mtrace ();
      signal (SIGUSR1, enable);
    }

    static void
    disable (int sig)
    {
      muntrace ();
      signal (SIGUSR2, disable);
    }

    int
    main (int argc, char *argv[])
    {
      ...

      signal (SIGUSR1, enable);
      signal (SIGUSR2, disable);

      ...
    }

I.e., the user can start the memory debugger any time s/he wants if the program was started with `MALLOC_TRACE` set in the environment. The output will of course not show the allocations which happened before the first signal but if there is a memory leak this will show up nevertheless.