Article ID: 92614
Article Last Modified on 12/11/2003
APPLIES TO
- Microsoft Visual C++ 1.0 Professional Edition
- Microsoft Visual C++ 1.5 Professional Edition
- Microsoft Visual C++ 1.51
- Microsoft Visual C++ 2.0 Professional Edition
- Microsoft Visual C++ 2.1
- Microsoft Visual C++ 4.0 Standard Edition
- Microsoft Visual C++ 5.0 Enterprise Edition
- Microsoft Visual C++ 5.0 Professional Edition
This article was previously published under Q92614
The sample source code below demonstrates how to initialize a const member of a class. Note that the code uses a member initialization list because a const member may not appear on the left side of the assignment operator. The value must be set when the object is constructed because the value of a const member can be set only at initialization.
If an application attempts to initialize a const member with the assignment operator, the compiler generates the following error messages:
Using Visual C++ 32-bit Edition, version 4.0, this error is reported as:
The member initialization list is the preferred method to initialize the members of a class. For example, when initializing an object of a user- defined type, it is more efficient to use a member initialization list to initialize a data member than to perform an assignment in the constructor. The latter approach requires two calls: one to construct the data member and another to the operator=() function to assign a value to the member.
Sample Code
/*
* Compile options needed: none
*/
#include <iostream.h>
class demo
{
const int a;
public:
demo(int val = 0) : a(val) {}
int get_a(void) { return a; }
};
void main()
{
demo first;
demo second(5);
cout << "First = " << first.get_a() << endl;
cout << "Second = " << second.get_a() << endl;
}
Output
First = 0
Second = 5
SUMMARY
Keywords: kbinfo kblangcpp KB92614
