Microsoft KB Archive/118679

{|
 * width="100%"|

PRB: Memory Leak Using Delete Operator

 * }

Q118679

-

The information in this article applies to:


 * Microsoft C/C++ for MS-DOS, version 7.0
 * Microsoft Visual C++, versions 1.0, 1.5

-

SYMPTOMS
When you release dynamically allocated memory back to the system by using the C++ delete operator in a QuickWin application, a memory leak occurs.

CAUSE
The run-time library provides four versions of the delete operator to deallocate pointers that are near, far, huge, or based. The version that is selected depends on the addressing mode of pointer. For example, if the pointer is a near pointer, the near delete operator is called. If the addressing mode of pointer does not reflect the version of the new operator used to allocate the memory, the incorrect version of the delete operator is called. For example:

  Node __far *fpN; fpN = new Node __near; // convert near to far delete fpn;            // far delete invoked for near object

Here, the compiler chooses the inappropriate delete operator for the pointer, which results in a run-time error.

RESOLUTION
To prevent this problem, explicitly cast the pointer to the addressing mode you want: 

  delete (Node __near *)fpN;

MORE INFORMATION
The following sample code can be used to demonstrate the memory leak. Replace the last two uncommented lines with the commented lines to see the correct output.

Sample Code
  /* Compile options needed: /Mq */   #include    #include    void main {     char * nearptr; char far * farptr; printf("\n"); printf("Starting memory: %u\n",_memavl); nearptr = new char; farptr = new char __near; // new returns a near pointer printf("After memory allocated: memavl=%u\n",_memavl); delete nearptr; // the near delete gets called delete farptr; // the far delete gets called for near memory printf("After memory is freed : memavl=%u\n",_memavl); //delete ( char __near *) farptr; // this will call the correct delete //printf("After memory is freed : memavl=%u\n",_memavl); } Additional query words: 7.00 1.00 1.50

Keywords : kb16bitonly kbprb

Issue type : kbprb

Technology : kbVCsearch kbAudDeveloper kbPTProdChange kbvc150 kbvc100 kbZNotKeyword3 kbCVC700DOS