VIRTUAL_BAD
Error in runtime initialization of virtual functions
Problem
Diagnosis (at runtime)
Repair

VIRTUAL_BAD

Error in runtime initialization of virtual functions

This error is caused when a virtual function has not been initialized prior to being used by another function.

Problem

The following pieces of code illustrate this error. The virtual function func is declared in virtbad1.C in the goo class. A static variable of this class, barney, is also declared in that file. The function crash calls func through barney in line 23. In file virtbad2.C, a static variable of class foo, fred, is declared. Class foo calls crash, which then in turn ends up calling the virtual function func. A virtual function's address is not established until the program is initialized at runtime, and static functions are also initialized at runtime. This means that depending on the order of initialization, fred could be trying to find func, which does not yet have an address. The VIRTUAL_BAD error message is generated when this code is compiled with Insure++.

Note: Due to differences in th object layout of different compilers. this error may not be detected with certain compilers.

	1: 	/*
	2:	 * File: virtbad1.C
	3:	 */
	4:	#include <iostream.h>
	5:
	6:	class goo {
	7:		public:
	8:		int i;
	9:		goo::goo() {
	10:			cerr << "goo is initialized."
					<< endl; }
	11:		virtual int func();
	12:		virtual int func2();
	13:	};
	14:	static goo barney;
	15:	int crash() {
	16:		int ret;
	17:		cerr << "Sizeof(goo) = " <<
					sizeof(goo) << endl;
	18:		cerr << "Sizeof(i) = " <<
					sizeof(int) << endl;
	19:		char *cptr = (char *) &barney;
	20:		cptr += 4;
	21:		long *lptr = (long *) cptr;
	22:		cerr << "vp = " << *lptr << endl;
	23:		ret = barney.func();
	24:		cerr << "crash" << endl;
	25:		return ret;
	26:	}
	27:	int goo::func() {
	28:		cerr << "goo.func" << endl;
	29:		func2(); 
	30:		return i;
	31:	}
	32:	int goo::func2() {
	33:		cerr << "goo.func2" << endl;
	34:		return 2;
	35:	}

	1:	/*
	2:	 * File: virtbad2.C
	3:	 */
	4:	#include <iostream.h>
	5:
	6:	extern int crash();
	7:
	8:	class foo {
	9:		public:
	10:		foo::foo() {
	11:			cerr << "foo" << endl;
	12:			cerr << "Got " <<
					crash() << endl;
	13:		}
	14:	};
	15:
	16:	static foo fred;

	1:	/*
	2:	 * File: virtbad3.C
	3:	 */
	4:	#include <iostream.h>
	5:
	6:	int main() {
	7:		cerr << "main" << endl;
	8:		return 0;
	9:	}

Diagnosis (at runtime)

   [virtbad1.C:29] **VIRTUAL_BAD**
1.   >>		func2();
	
2.	Virtual function table is invalid: func2()
	
3.	Stack trace where the error occurred:
				goo::func()	virtbad1.C, 29
				    crash()	virtbad1.C, 23
				 foo::foo()	virtbad2.C, 12
	__mod_I__fred0virtbad21001_cc_000()	
				    _main()	
				     main()	virtbad3.C, 6

   **Memory corrupted. Program may crash!!**
4.   Abort (core dumped)

1. Source line at which the problem was detected.
2. Description of the problem and which virtual function caused the error.
3. Stack trace showing the function call sequence leading to the error.
4. Core dumps typically follow these messages, as any usage of the dynamic memory functions will be unable to cope.

Repair

The error in the sample code could be eliminated by not making fred static. In that case, the address for func would be generated during the initialization before any requests for it existed, and there would be no problems.

USER_ERROR

WRITE_BAD_INDEX