libexception

Author

Benedikt Böhm

Version

0.2_beta

Web

http://github.com/hollow/libexception

Git

git clone https://github.com/hollow/libexception.git

Download

http://github.com/hollow/libexception/downloads

libexception is an exception handling library for C. It uses the setjmp and longjmp calls to build a stack of jump buffers and exceptions and provides high level semantics implemented as macros to make exception handling in C unobtrusive and easy to use.

Rationale

Error handling is an important issue in programming languages, and it can account for a substantial portion of a project's code. The classic C approach to this problem is return codes. Each function returns a value indicating success or failure. However, with a nontrivial function call hierarchy, this approach clutters the code significantly. Every function must check the return code of every function call it makes and take care of errors. In most cases, the function will merely pass any errors back up to its caller.

Programming languages such as Ada or C++ address this issue with exceptions. Exceptions make it easy to separate error handling from the rest of the code. Intermediate functions can completely ignore errors occurring in functions they call, if they can't handle them anyway.

The solution to this problem is to implement a simple exception-handling library in C.

Implementation

libexception uses two stacks implemented as a doubly-linked list to record exceptions and jump buffers needed by setjmp/longjmp. The work-flow is as follows:

1. try will call setjmp and push the resulting jmp_buf object onto the tryenv stack.
2. usually setjmp returns zero and the following block is executed. if no exception occured nothing else happens.
3. if an exception is raised throw will push information about the error onto the exception stack and call longjmp to jump to the topmost tryenv buffer.
4. in this case setjmp returns again, but with a non-zero return code and the following except block is executed.
5. an except block consists of zero or more on blocks to handle a single exception and zero or one finally block to handle a yet unhandled but unknown exception
6. if an on block handled the exception the exception stack is cleared and nothing else happens.
7. if no on block handled the exception but a finally block handled the exception the exception stack is cleared and nothing else happens.
8. if an unhandled exception is found at the end of an except block, control is transfered to the next jump buffer (a.k.a except block).
9. if there are no more jump buffers available, the default exception handler is called to print an exception trace to STDERR and the program will be aborted.

Installation

To install libexception call ./configure, then make and finally make install.

Documentation

The libexception API reference can be found on-line or in PDF.

Examples

Examples can be found in the test-suite.