CWG Issue 98 (original) (raw)

This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 118e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2025-11-05

98. Branching into try block

Section: Clause 14 [except]Status: TC1Submitter: Jack RouseDate: 23 Feb 1999

At the top of clause 15, in paragraph 2, it says:

A goto, break, return, or continue statement can be used to transfer control out of a try block or handler, but not into one.

What about switch statements?

switch ( f() )
{
case 1:
     try {
         g();
case 2:
         h();
     }
     catch (...)
     {
         // handler
     }
break;
}

Daveed Vandevoorde:

Consider:

void f() {
    try {
    label:
        ;
    } catch(...) {
        goto label;
    }
}

Now the phrase "try block" (without a hyphen) is used in paragraph 1 in a way that causes me to think that it is not intended to include the corresponding handlers. On the other hand, the grammar entity "try-block" (with hyphen) does include the handlers. So is the intent to prohibit the above or not?

Proposed resolution (10/00:

Change text in Clause 14 [except] paragraph 2 from:

A goto, break, return, orcontinue statement can be used to transfer control out of a try block or handler, but not into one.

to:

A goto or switch statement shall not be used to transfer control into a try block or into a handler.
[ Example:

void f() {
goto l1; // Ill-formed
goto l2; // Ill-formed
try {
goto l1; // OK
goto l2; // Ill-formed
l1: ;
} catch (...) {
l2: ;
goto l1; // Ill-formed
goto l2; // OK
}
}

—end example ]
A goto, break, return, or continuestatement can be used to transfer control out of a try block or handler.

(See also issue 246.)