FIX: Constructor Gets Called Multiple Times on the Same Object (152211)


The information in this article applies to:

  • Microsoft Visual C++, 32-bit Editions 4.1
  • Microsoft Visual C++, 32-bit Enterprise Edition 4.2
  • Microsoft Visual C++, 32-bit Enterprise Edition 5.0
  • Microsoft Visual C++, 32-bit Enterprise Edition 6.0
  • Microsoft Visual C++, 32-bit Professional Edition 4.2
  • Microsoft Visual C++, 32-bit Professional Edition 5.0
  • Microsoft Visual C++, 32-bit Professional Edition 6.0
  • Microsoft Visual C++, 32-bit Learning Edition 6.0
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
Modification Type:MinorLast Reviewed:7/5/2005
Keywords:kbBug kbCompiler kbCPPonly kbfix kbNoUpdate KB152211
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