Article ID: 149966
Article Last Modified on 12/10/2003
APPLIES TO
- The C Run-Time (CRT), when used with:
- Microsoft Visual C++ 1.52 Professional Edition
- Microsoft Visual C++ 2.0 Professional Edition
- Microsoft Visual C++ 2.1
- Microsoft Visual C++ 2.2
- Microsoft Visual C++ 4.0 Standard Edition
- Microsoft Visual C++ 4.1 Subscription
- Microsoft Visual C++ 4.2 Enterprise Edition
- Microsoft Visual C++ 5.0 Enterprise Edition
- Microsoft Visual C++ 6.0 Enterprise Edition
- Microsoft Visual C++ 4.2 Professional Edition
- Microsoft Visual C++ 5.0 Professional Edition
- Microsoft Visual C++ 6.0 Professional Edition
- Microsoft Visual C++ 6.0 Standard Edition
- Microsoft Visual C++ .NET 2002 Standard Edition
This article was previously published under Q149966
SYMPTOMS
If an error occurs when extracting long values from the stream, the error cannot be cleared and other streams also report errors.
CAUSE
When the istream::operator>>(long& n) encounters an error, it sets ios::failbit, but does not clear errno. This causes the stream to continue to fail even after ios::clear is called. It also causes other streams to fail.
RESOLUTION
To work around the bug, set errno to zero in addition to completing normal stream error checking.
STATUS
This bug was corrected in Microsoft Visual C++ .NET 2003.
MORE INFORMATION
Sample Code
/*
The following sample code demonstrates only the bug and workaround, not
normal error checking.
Compile options needed: none
*/
#include <iostream.h>
#include <strstrea.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_STRING_LEN 100
//#define CLEAR_ERRNO // uncomment to work around bug
void main()
{
char dc1a, dc1b, dc2a, dc2b;
long input1a=0, input1b=0;
long input2a=0, input2b=0;
char szTest1[MAX_STRING_LEN];
char szTest2[MAX_STRING_LEN];
strcpy(szTest1,"a2147483648z50"); //
strcpy(szTest2,"a500z50");
istrstream StrStream1(szTest1); //String stream 1
istrstream StrStream2(szTest2); //String stream 2
// The following command will fail since value input to
// input1a=2147483648 is
// bigger that maximum value long can hold.
StrStream1 >> dc1a >> input1a >> dc1b >> input1b;
#ifdef CLEAR_ERRNO
errno = 0;
#endif
StrStream2 >> dc2a >> input2a >> dc2b >> input2b;
cout << "\n dc1a: " << dc1a
<< "\n input1a: " << input1a
<< "\n dc1b: " << dc1b
<< "\n input1b: " << input1b << endl;
cout << "\n dc2a: " << dc2a
<< "\n input2a: " << input2a
<< "\n dc2b: " << dc2b
<< "\n input2b: " << input2b << endl;
cout << "\n\nPress any key to continue..." << endl;
dc1a = getchar();
}
/*
The output is:
dc1a: a
input1a: 2147483647
dc1b:
input1b: 0
dc2a: a
input2a: 500
dc2b:
input2b: 0
If CLEAR_ERRNO is set, the output is as expected:
dc1a: a
input1a: 2147483647
dc1b:
input1b: 0
dc2a: a
input2a: 500
dc2b: z
input2b: 50
*/
Additional query words: kbVC400bug
Keywords: kbfix kbcrt KB149966
