There are three versions of the Allegro library: the normal optimised code, one with extra debugging support, and a profiling version. See the platform specific readme files for information about how to install and link with these alternative libs. Although you will obviously want to use the optimised library for the final version of your program, it can be very useful to link with the debug lib while you are working on it, because this will make debugging much easier, and includes assert tests that will help to locate errors in your code at an earlier stage. Allegro also contains some debugging helper functions:
void al_assert(const char *file, int line);
Raises an assert for an error at the specified file and line number. The
file parameter is always given in ASCII format. If you have installed a
custom assert handler it uses that, or if the environment variable
ALLEGRO_ASSERT is set it writes a message into the file specified by the
environment, otherwise it aborts the program with an error message. You
will usually want to use the ASSERT() macro instead of calling this
function directly.
void al_trace(const char *msg, ...);
Outputs a debugging trace message, using a printf() format string given
in ASCII. If you have installed a custom trace handler it uses that, or
if the environment variable ALLEGRO_TRACE is set it writes into the file
specified by the environment, otherwise it writes the message to
"allegro.log" in the current directory. You will usually want to use the
TRACE() macro instead of calling this function directly.
void ASSERT(condition);
Debugging helper macro. Normally compiles away to nothing, but if you
defined the preprocessor symbol DEBUGMODE before including Allegro headers,
it will check the supplied condition and call al_assert() if it fails.
void TRACE(char *msg, ...);
Debugging helper macro. Normally compiles away to nothing, but if you
defined the preprocessor symbol DEBUGMODE before including Allegro headers,
it passes the supplied message given in ASCII format to al_trace().
void register_assert_handler(int (*handler)(const char *msg));
Supplies a custom handler function for dealing with assert failures. Your
callback will be passed a formatted error message in ASCII, and should
return non-zero if it has processed the error, or zero to continue with
the default actions. You could use this to ignore assert failures, or to
display the error messages on a graphics mode screen without aborting the
program.
void register_trace_handler(int (*handler)(const char *msg));
Supplies a custom handler function for dealing with trace output. Your
callback will be passed a formatted error message in ASCII, and should
return non-zero if it has processed the message, or zero to continue with
the default actions. You could use this to ignore trace output, or to
display the messages on a second monochrome monitor, etc.