likon / cexception Goto Github PK

====================================================================
CException
====================================================================

CException is a basic exception framework for C, suitable for use in
embedded applications.  It provides an exception framework similar in
use to C++, but with much less overhead.

CException uses C standard library functions setjmp and longjmp to 
operate.  As long as the target system has these two functions defined,
this library should be useable with very little configuration.  It 
even supports environments where multiple program flows are in use, 
such as real-time operating systems.

There are about a gabillion exception frameworks using a similar 
setjmp/longjmp method out there... and there will probably be more 
in the future. Unfortunately, when we started our last embedded 
project, all those that existed either (a) did not support multiple 
tasks (therefore multiple stacks) or (b) were way more complex than 
we really wanted.  CException was born.

Why use CException?

0. It's ANSI C, and it beats passing error codes around.

1. You want something simple... CException throws a single id. You can 
   define those ID's to be whatever you like. You might even choose which 
   type that number is for your project. But that's as far as it goes. 
   We weren't interested in passing objects or structs or strings... 
   just simple error codes.

2. Performance... CException can be configured for single tasking or 
   multitasking. In single tasking, there is very little overhead past 
   the setjmp/longjmp calls (which are already fast). In multitasking, 
   your only additional overhead is the time it takes you to determine 
   a unique task id 0 - num_tasks. 

For the latest version, go to http://cexception.sourceforge.net

--------------------------------------------------------------------
CONTENTS OF THIS DOCUMENT
--------------------------------------------------------------------

Usage
Limitations
API
Configuration
Testing
License

--------------------------------------------------------------------
Usage
--------------------------------------------------------------------

Code that is to be protected are wrapped in Try { } Catch { } blocks.
The code directly following the Try call is "protected", meaning that
if any Throws occur, program control is directly transferred to the
start of the Catch block.

A numerical exception ID is included with Throw, and is made accessible
from the Catch block.

Throws can occur from within function calls (nested as deeply as you 
like) or directly from within the function itself.

--------------------------------------------------------------------
Limitations
--------------------------------------------------------------------

This library was made to be as fast as possible, and provide basic
exception handling.  It is not a full-blown exception library.  Because 
of this, there are a few limitations that should be observed in order 
to successfully utilize this library:

1. Do not directly "return" from within a Try block, nor "goto" 
   into or out of a Try block.  
   
   Why? 
   
   The "Try" macro allocates some local memory and alters a global 
   pointer.  These are cleaned up at the top of the "Catch" macro. 
   Gotos and returns would bypass some of these steps, resulting in
   memory leaks or unpredictable behavior.
   
2. If (a) you change local (stack) variables within your Try block, 
   AND (b) wish to make use of the updated values after an exception 
   is thrown, those variables should be made volatile. Note that this 
   is ONLY for locals and ONLY when you need access to them after a 
   throw.
   
   Why?
   
   Compilers optimize.  There is no way to guarantee that the actual 
   memory location was updated and not just a register unless the 
   variable is marked volatile.

3. Memory which is malloc'd or new'd is not automatically released
   when an error is thrown.  This will sometimes be desirable, and
   othertimes may not.  It will be the responsibility of the Catch
   block to perform this kind of cleanup.
   
   Why?
   
   There's just no easy way to track malloc'd memory, etc., without
   replacing or wrapping malloc calls or something like that.  This 
   is a light framework, so these options were not desirable.
   
--------------------------------------------------------------------
API
--------------------------------------------------------------------

Try
---

Try is a macro which starts a protected block.  It MUST be followed by 
a pair of braces or a single protected line (similar to an 'if'), 
enclosing the data that is to be protected.  It MUST be followed by a 
Catch block (don't worry, you'll get compiler errors to let you know if 
you mess any of that up).

Catch(e)
--------

Catch is a macro which ends the Try block and starts the error handling 
block. The catch block is called if and only if an exception was thrown 
while within the Try block.  This error was thrown by a Throw call 
somewhere within Try (or within a function called within Try, or a function
called by a function called within Try, etc).

The single parameter 'e' is filled with the error code which was thrown.
This can be used for reporting, conditional cleanup, etc. (or you can just
ignore it if you really want... people ignore return codes all the time, 
right?).  'e' should be of type EXCEPTION_T;

Throw(e)
--------

The method of throwing an error.  Throws should only occur from within a
protected (Try...Catch) block, though it may easily be nested many function
calls deep without an impact on performance or functionality.  Throw takes 
a single argument, which is an exception id which will be passed to Catch 
as the reason for the error.

If you wish to Rethrow an error, this can be done by calling Throw(e) with
the error code you just caught.  It IS valid to throw from a catch block.

--------------------------------------------------------------------
CONFIGURATION
--------------------------------------------------------------------

CException is a mostly portable library.  It has one universal 
dependency, and some macros which are required if working in a 
multi-tasking environment.

1. The standard C library setjmp must be available.  Since this is part
   of the standard library, chances are good that you'll be fine.

2. If working in a multitasking environment, methods for obtaining an 
   index into an array of frames and to get the overall number of 
   id's are required.  If the OS supports a method to retrieve Task 
   ID's, and those Tasks are number 0, 1, 2... you are in an ideal 
   situation.  Otherwise, a more creative mapping function may be 
   required.  Note that this function is likely to be called twice 
   for each protected block and once during a throw.  This is the 
   only overhead in the system.
   
Exception.h
-----------------
By convention, most projects include Exception.h which defines any 
further requirements, then calls CException.h to do the gruntwork.  All
of these are optional.  You could directly include CException.h if
you wanted and just use the defaults provided.

EXCEPTION_T      - Set this to the type you want your exception id's 
                   to be.  Defaults to 'unsigned int'.

EXCEPTION_NONE   - Set this to a number which will never be an 
                   exception id in your system.  Defaults to 0x5a5a5a5a.

EXCEPTION_GET_ID - If in a multi-tasking environment, this should be 
                   set to be a call to the function described in #2 above.
                   Defaults to just return 0 all the time (good for 
                   single tasking environments)
                     
EXCEPTION_NUM_ID - If in a multi-tasking environment, this should be set
                   to the number of ID's required (usually the number of
                   tasks in the system).  Defaults to 1 (for single
                   tasking environments).

CEXCEPTION_NO_CATCH_HANDLER(id) - This macro can be optionally specified.  
                   It allows you to specify code to be called when a Throw 
                   is made outside of Try...Catch protection.  Consider 
                   this the emergency fallback plan for when something has 
                   gone terribly wrong.

You may also want to include any header files which will commonly be
needed by the rest of your application where it uses exception handling 
here.  For example, OS header files or exception codes would be useful.

--------------------------------------------------------------------
TESTING
--------------------------------------------------------------------

If you want to validate that CException works with your tools or that
it works with your custom configuration, you may want to run the test
suite.

The test suite included makes use of the Unity Test Framework.  It will
require a native C compiler. The example makefile uses MinGW's gcc.  
Modify the makefile to include the proper paths to tools, then run 'make'
to compile and run the test application.  

C_COMPILER - The C compiler to use to perform the tests
C_LIBS - The path to the C libraries (including setjmp) 
UNITY_DIR - The path to the Unity framework (required to run tests)
            (get it at http://unity.sourceforge.net)

--------------------------------------------------------------------
LICENSE
--------------------------------------------------------------------

This software is licensed under the MIT License

Copyright (c) 2007-2012 Mark VanderVoord

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.