Article ID: 152211
Article Last Modified on 7/5/2005
APPLIES TO
- Microsoft Visual C++ 4.1 Subscription
- Microsoft Visual C++ 4.2 Enterprise Edition
- Microsoft Visual C++ 5.0 Enterprise Edition
- Microsoft Visual C++ 6.0 Enterprise Edition
- Microsoft Visual C++ 4.2 Professional Edition
- Microsoft Visual C++ 5.0 Professional Edition
- Microsoft Visual C++ 6.0 Professional Edition
- Microsoft Visual C++ 6.0 Standard Edition
This article was previously published under Q152211
SYMPTOMS
The constructor gets called more than once on the same global object.
CAUSE
This error occurs when a file has both a global object and a function that references the global object as extern. In this case, the compiler incorrectly generates code that calls the constructor on the "extern myClass object;" statement.
RESOLUTION
Remove the line that contains extern reference to the global. You can safely remove this line since the global is in file scope.
-or-
Create two separate files, one that contains the global object, and one that contains the function that references the global object as extern.
STATUS
Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.
This problem was corrected in Microsoft Visual C++ .NET.
MORE INFORMATION
Sample Code
// This sample demonstrates the problem of the constructor getting
// called twice.
/* Compile options needed: cl test.cpp
*/
// TEST.CPP
// ========
#include "stdio.h"
class myClass {
public:
myClass() {printf("myClass Constructor called\n");};
void test() {printf("test() called\n");};
} object;
void main()
{
// Remove the next line for the first workaround:
extern myClass object;
object.test();
}
// sample output: (without extern line removed)
myClass Constructor called
myClass Constructor called
test() called
// This sample demonstrates the workaround that causes the program
// to only call the constructor once.
/* Compile options needed: cl Test2A.cpp Test2B.cpp
*/
// Test2.h
// ========
#include "stdio.h"
class myClass {
public:
myClass() {printf("myClass Constructor called\n");};
void test() {printf("test() called\n");};
};
// Test2A.cpp
// ==========
#include "Test2.h"
myClass object;
// Test2B.cpp
// ==========
#include "Test2.h"
void main()
{
extern myClass object;
object.test();
}
// sample output:
myClass Constructor called
test() called
Additional query words: 10.10 10.20
Keywords: kbbug kbfix kbnoupdate kbcpponly kbcompiler KB152211
