Cleanups

Cleanups are a structured way to deal with things that need to be done later. When your code does something (like malloc some memory, or open a file) that needs to be undone later (e.g. free the memory or close the file), it can make a cleanup. The cleanup will be done at some future point: when the command is finished, when an error occurs, or when your code decides it's time to do cleanups.

You can also discard cleanups, that is, throw them away without doing what they say. This is only done if you ask that it be done.

Syntax:

struct cleanup *old_chain;

Declare a variable which will hold a cleanup chain handle.

old_chain = make_cleanup (function, arg);

Make a cleanup which will cause function to be called with arg (a char *) later. The result, old_chain, is a handle that can be passed to do_cleanups or discard_cleanups later. Unless you are going to call do_cleanups or discard_cleanups yourself, you can ignore the result from make_cleanup.

do_cleanups (old_chain);

Perform all cleanups done since make_cleanup returned old_chain. E.g.:

make_cleanup (a, 0); 
old = make_cleanup (b, 0); 
do_cleanups (old);

will call b() but will not call a(). The cleanup that calls a() will remain in the cleanup chain, and will be done later unless otherwise discarded.

discard_cleanups (old_chain);

Same as do_cleanups except that it just removes the cleanups from the chain and does not call the specified functions.

Some functions, e.g. fputs_filtered() or error(), specify that they "should not be called when cleanups are not in place". This means that any actions you need to reverse in the case of an error or interruption must be on the cleanup chain before you call these functions, since they might never return to your code (they `longjmp' instead).