Article ID: 125309
Article Last Modified on 11/21/2006
APPLIES TO
- Microsoft Foundation Class Library 4.2, when used with:
- Microsoft Visual C++ 1.0 Professional Edition
- Microsoft Visual C++ 1.5 Professional Edition
- Microsoft Visual C++ 1.51
- Microsoft Visual C++ 1.0 Professional Edition
This article was previously published under Q125309
SYMPTOMS
If new is called to allocate an array whose size is determined by a variable that has a value of zero (0), the program terminates with the following message in a debug build:
The <line> value depends on the version of MFC that you have:
- In MFC 2.0 <line> = 275
- In MFC 2.1 <line> = 267
- In MFC 2.5 <line> = 277
- In MFC 2.51 <line> = 286
In MFC 3.x, the code generates a TRACE message similar to this:
RESOLUTION
This behavior changed with the introduction of Visual C++ version 2.0. In the MFC that shipped with version 2.0, a TRACE is output to the Debug Window in Debug mode.
If you encounter the assertion failure, you can work around it by simply not calling new for a zero-length array. Check for a zero value before calling new. If you need to have a valid address for the memory block, allocate an array of size 1 as in new[1].
STATUS
This behavior is by design. It is intended to help programmers detect logic errors in programs.
MORE INFORMATION
The run-time operator new() can be called with the argument zero. A distinct (non-null) pointer to an object will be returned. (See Section 5.3.3, third paragraph of the ARM - M.A.Ellis, B.Stroustrup.) This is the behavior of Visual C++ versions 2.x and 4.0. However, Visual C++ version 4.0 does not warn when new() is called with a zero size. It is the programmer's responsibility to ensure the pointer returned by new() is of the appropriate size.
Sample Code
/* Compile options needed:
Default MFC App.
*/
int size=0;
char * p = new char[size];
// With MFC 2.51 or earlier, this causes an Assert to be thrown
// With MFC 3.x this causes a TRACE warning
Additional query words: 1.00 1.50 2.00 2.10 2.50 2.51
Keywords: kbnoupdate kbprb KB125309
