COMMAND_PARSE_OPTIONAL_NUMBER macro

parses the command argument at position @a argn into @a out as a @a type if the argument @a argn does not start with '-'. and passes the error code to the caller. @a argn will be incremented if no error occurred. Otherwise the calling function will return the error code produced by the parsing function. This function may cause the calling function to return immediately, so it should be used carefully to avoid leaking resources. In most situations, parsing should be completed in full before proceeding to allocate resources, and this strategy will most prevents leaks.