NewLC - TRAPs and Leaves - Comments

> TRAPs and Leaves

Inder — Thu, 18 Jan 2007 03:50:53 +0100

Try Catch is not used in Symbian because of one more very important Reason, * It produces a lot of RAM overhead and also adds on considerably to the size of the compiled code. Thus The compilers are directed specifiaclly to Flag an error if C++ exeception handling is used.

how to execute the statement, when leave happens

eric — Tue, 19 Dec 2006 09:17:23 +0100

You should use a trap harness to do this and rename your Exe() function to ExeL() to indicate it can leave (the latter won't change anything in how the code behaves but will give an indication to other users of your code).

TInt res=KErrUnknown; TRAPD(leaveCause, res=ptr->ExeL()); if(res==(xxxx)) { // success } else { // error // use res and leaveCause to get further information }

how to execute the statement, when leave happens

pacuboit — Tue, 19 Dec 2006 06:16:43 +0100

Hi below is snap of code

ptr->ExecutecodeL( xxx); if (ptr->Exe() == (xxx) _LIT("success"); else _LIT("Error");

when i execute function ptr->Exe() function will leave. so I want to execute statement "_LIT("success");" even if it leaves. How can i implement this.

> like exceptions?

Mr Big — Tue, 02 Nov 2004 00:39:29 +0100

It is very similar to Exceptions. The Symbian Leave and Trap pattern was established before C++ support for exceptions was finalised and correctly supported in gcc.

Trap and leave are used for rolling back operations. And the rules of writing exception safe code apply equally to leaves. So brush up on the lessons of C++ gurus such as Herb sutter.

leave do have limitations compared with exceptions.

1. You can only leave with a TInt error code. exceptions can throw any kind of object, which offers the possiblity to throw more context.

2. Destructors are not called leaves are implemented in a similar way to long jumps which means that destructors of stack based objects will not be called as a result of an exception. To get around this, the leave mechanism is complemented by the cleanup stack. On leave, anything that needs to be destroyed in order to achive successful rollback (and freeing of resources) should be pushed on the cleanup stack. The cleanup stack is a manager object and used in roughly the same way as TAutoPtr. See the link

3. Leave safety is not enforced by the compiler. Ony a naming convention is used to denote the exception API.

With the forthcoming support for EABI binary inferface and rich compilers, Symbian will need to move over to a more industry standard exception mechanism.

> TRAPs and Leaves, here'

Anonymous — Tue, 01 Jun 2004 13:42:21 +0200

No try-catch was available when Symbian was originally developed. AFAIK. (I read this from a magazine months ago.)

And now that we have this nice TRAP thingy, and it is widely used, we don't even want to change to try-catch!

> TRAPs and Leaves

gg — Thu, 13 May 2004 03:17:17 +0200

void MyControl::Draw(const TRect& aRect) throw() ... try MyLeavingFunctionL()); catch(...) ...

what is diff?

> TRAPs and Leaves

gg — Thu, 13 May 2004 03:12:06 +0200

why not try-catch?

like exceptions?

S Woodside — Sun, 07 Mar 2004 09:03:04 +0100

So this is very similar to try and exception handling is it not? similarities? differences?

TRAPs and Leaves

eric — Fri, 07 Mar 2003 14:50:03 +0100