Knowledge Base

FIX: Using String Constant as Default Argument Doesn't Work

Article ID: 124524

Article Last Modified on 7/5/2005

Microsoft Visual C++ 2.0 Professional Edition, when used with:
- the hardware: Intel x86

This article was previously published under Q124524

SYMPTOMS

Using a string constant to initialize a character pointer as a default parameter argument in a class member function does not work as expected. Instead of assigning the address of the string constant to the pointer, the compiler uses a different existing string constant.

CAUSE

This is a problem with character constants within a class definition, no matter how they are used. The compiler always uses the last string constant in the class definition.

RESOLUTION

To work around the problem, create a static character pointer that is set to the desired string constant and use that static variable to initialize the character pointer parameter of the constructor. Typically, string constants are defined globally in a header file so that they can be easily modified.

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++, 32-bit Edition, version 4.0.

MORE INFORMATION

You can use the following sample to reproduce this problem. The output of the sample code will be:

Value of 'String' 1234567890 = 123456

In this case, the compiler used the first six characters of the "1234567890" string instead of using the "abcde" string.

Sample Code

/* Compile options needed: none
*/ 

#include <iostream.h>

class A
{
public:
   void Func(char* String = "abcde")
   {
      cout << "Value of 'String' " << "1234567890 = " << String << endl;
   }
};

void main()
{
   A a;
   a.Func();
}

Additional query words: 2.00 9.00 buglist2.00

Keywords: kbbug kbfix kbcpponly kbcompiler KB124524