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c++/2659: bad_cast exception not thrown
- To: <gcc-gnats at gcc dot gnu dot org>
- Subject: c++/2659: bad_cast exception not thrown
- From: "Uwe F. Mayer" <mayer at tux dot org>
- Date: Thu, 26 Apr 2001 16:49:27 -0400 (EDT)
>Number: 2659
>Category: c++
>Synopsis: bad_cast exception not thrown
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Thu Apr 26 13:56:01 PDT 2001
>Closed-Date:
>Last-Modified:
>Originator: Uwe F. Mayer
>Release: 3.0 20010409 (prerelease)
>Organization:
tux.org
>Environment:
System: Linux tosca 2.2.18 #2 Thu Mar 8 13:48:25 PST 2001 i686 unknown
Architecture: i686
host: i686-pc-linux-gnu
build: i686-pc-linux-gnu
target: i686-pc-linux-gnu
configured with: ../gcc/configure --prefix=/usr/local/gcc --disable-nls
>Description:
g++ does not throw a bad_cast exception when a base-class pointer is
dynamically cast to a derived-class pointer, which of course is illegal.
It does, however, return a NULL pointer which was the old style error
condition detection.
>How-To-Repeat:
Compile this program with "g++ bad_cast.cpp" and run it.
Gives a Segmentation fault.
Source code below:
/**********************************************************************
Filename: bad_cast.cpp
Chapter: 9 Exceptions
Compiler: Borland C++ Version 5.01 Summer 1998
C++ for C Programmers, Edition 3 By Ira Pohl
********************************************************************/
#include <iostream>
#include <exception>
#include <typeinfo>
using namespace std;
class A {
public:
virtual void foo() { cout << "in A" << endl; }
};
class B: public A {
public:
void foo() { cout << "in B" << endl; }
};
int main()
{
try {
A a, *pa; B b, *pb;
pa = &b;
pb = dynamic_cast<B*>(pa); //succeeds
pb -> foo();
pa = &a;
pb = dynamic_cast<B*>(pa); //fails
// if (pb==NULL) {bad_cast x; throw x; } // my g++ does not throw it
pb -> foo();
}
catch(bad_cast) { cout << "dynamic_cast failed" << endl; }
}
>Fix:
Work around: Use the old style NULL-pointer test and throw the exception
yourself.
>Release-Note:
>Audit-Trail:
>Unformatted: