libstdc++/10674: fstream fails to open files in in/out mode if file doesn't exist

[daniel.lemire@nrc.gc.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: