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libstdc++/10674: fstream fails to open files in in/out mode if file doesn't exist
- From: daniel dot lemire at nrc dot gc dot ca
- To: gcc-gnats at gcc dot gnu dot org
- Date: 8 May 2003 01:36:23 -0000
- Subject: libstdc++/10674: fstream fails to open files in in/out mode if file doesn't exist
- Reply-to: daniel dot lemire at nrc dot gc dot ca
>Number: 10674
>Category: libstdc++
>Synopsis: fstream fails to open files in in/out mode if file doesn't exist
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: unassigned
>State: open
>Class: sw-bug
>Submitter-Id: net
>Arrival-Date: Thu May 08 01:46:00 UTC 2003
>Closed-Date:
>Last-Modified:
>Originator: daniel.lemire@nrc.gc.ca
>Release: gcc version 3.4 20030507 (experimental) + gcc version 3.2.3
>Organization:
>Environment:
linux 2.4.18-3 (RedHat 7.3) on 686
>Description:
If one wants to open a file for random access (in/out)
so that the compiler automatically createst the file
when the file doesn't exist, one would do
fstream s("test.txt",ios::in |ios::out);
This will fail if fstream when the file doesn't exist.
It didn't fail with previous compilers (pre 3.x series).
>How-To-Repeat:
given the file test.cpp below
===================
#include <fstream>
using namespace std;
int main() {
fstream s("test.txt",ios::in | ios::out);
if(!s.is_open()) cout << "bug!"<<endl;
return 0;
}
===============
do
g++ -o a.out test.cpp -O2
followed by
./a.out
make sure test.txt doesn't exist and you'll
get
bug!
>Fix:
Revert back to gcc 2.96 or else
FileStream->open( FileName, std::ios::in | std::ios::out);
if(! FileStream->is_open()) {
FileStream->clear();
FileStream->open( FileName, std::ios::in | std::ios::out| std::ios::trunc);
}
since the trunc (truncate) apparently allows you to
create a file if none is present.
The code above is obviously very ugly.
>Release-Note:
>Audit-Trail:
>Unformatted: