ExceptionHandling.h File Reference

Java-like exceptions for C. More...

#include <setjmp.h>
#include <string.h>

Go to the source code of this file.

Defines
#define	try
	Start execution of code which might throw an exception that might be caught by the exception handlers that follow this try.
#define	catch(X)
	Define an exception handler.
#define	catchAll()
	Define a default exception handler.
#define	endtry
	End exception handling.
#define	throw(X)
	Throw an exception.
#define	rethrow()   throw(exception)
	Rethrows the current exception.
#define	throws(X)
	Declare that a function throws an exception of this type.
Variables
jmp_buf *	currentExceptionBuffer
	The exception buffer of the current thread.

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Detailed Description

Java-like exceptions for C.

This is part of AceUnit but can also be used without AceUnit.

Example:

 #define SomeException 1
 int someMethod() throws(SomeException) {
     if (someCondition) {
         throw(SomeException);
     }
 }

 int someCaller() {
     try {
         someMethod();
     } catch (SomeException) {
         // handle this exception
     } endtry;
 }
 

Differences to Java

• Exceptions are only int values.
• endtry MUST not be omitted.
• Omitting the {} block at try or catch will eventually not be detected by the compiler but lead to extremely strange behaviour.
• throw has a slightly different syntax.
• throws has a slightly different syntax and currently no effect.
• there are no checked exceptions, i.e. exception handling cannot be enforced.

Similarities with Java

• You can have more than one catch clause per try.
• You can have zero or more catch clauses per try. Yes, having zero catch clauses is allowed. But unlike Java this doesn't make sense in C.

Author:

Christian Hujer

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Define Documentation

#define catch

(

X

)

Value:

while (false); \
            break; \
        case (X): exception = 0; do \

Define an exception handler.

Parameters:

X

exception to catch, MUST be of type int.

 

#define catchAll

(

)

Value:

while (false); \
            break; \
        default: exception = 0; do \

Define a default exception handler.

#define endtry

Value:

while (false); \
        } \
        currentExceptionBuffer = prev; \
        if (exception) { \
            longjmp(*currentExceptionBuffer, exception); \
        } \
    } while(0)

End exception handling.

 

#define rethrow

(

)

throw(exception)

Rethrows the current exception.

This is a shorthand for throw(exception).

#define throw

(

X

)

Value:

do { \
        longjmp(*currentExceptionBuffer, (X)); \
    } while (false)

Throw an exception.

Parameters:

X

Exception to throw, MUST be of type int.

#define throws

(

X

)

Declare that a function throws an exception of this type.

This is currently unused but might be used in future by additional tools that could look for uncaught exceptions.

Parameters:

X

Exception type to declare, MUST be of type int.

#define try

Value:

do { \
        int exception; \
        jmp_buf lbuf; \
        jmp_buf *prev = currentExceptionBuffer; \
        currentExceptionBuffer = &lbuf; \
        switch (exception = setjmp(lbuf)) { \
        case 0: do \

Start execution of code which might throw an exception that might be caught by the exception handlers that follow this try.

From catch / catchAll to endtry, a local variable named exception will exist and contain the exception information (that is, setjmp() return value).

Warning:

Never omit endtry

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Variable Documentation

jmp_buf* currentExceptionBuffer

The exception buffer of the current thread.

If you work in a multi-threaded environment, make sure the scheduler allocates a jmp_buf for each thread and initializes currentExceptionBuffer for that thread with each conext switch. If you don't, your system will get very upset about interrupted exceptions.

Make sure that the scheduler starts each thread with an initialized jmp_buf (invoke setjmp() once!), otherwise your system will get very upset about uncaught exceptions.

If you work in a single-threaded environment, still make sure that setjmp(*currentExceptionBuffer) is invoked at least once at the very beginning, otherwise your system will get very upset about uncaught exceptions.

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