This is the mail archive of the
gcc-bugs@gcc.gnu.org
mailing list for the GCC project.
Re: libstdc++/6746: ifstream::readsome() always returns zero
- From: bkoz at gcc dot gnu dot org
- To: bkoz at gcc dot gnu dot org, gcc-bugs at gcc dot gnu dot org, gcc-prs at gcc dot gnu dot org, tony dot oliver at mci dot co dot uk
- Date: 5 Jul 2002 00:39:54 -0000
- Subject: Re: libstdc++/6746: ifstream::readsome() always returns zero
- Reply-to: bkoz at gcc dot gnu dot org, bkoz at gcc dot gnu dot org, gcc-bugs at gcc dot gnu dot org, gcc-prs at gcc dot gnu dot org, tony dot oliver at mci dot co dot uk, gcc-gnats at gcc dot gnu dot org
Synopsis: ifstream::readsome() always returns zero
State-Changed-From-To: analyzed->open
State-Changed-By: bkoz
State-Changed-When: Thu Jul 4 17:39:53 2002
State-Changed-Why:
It looks like I am not going to be able to fix this before I leave. I'll resume looking at it after I get back, say July 23 rd ish...
In sum, it looks like the patch to libstdc++/3647 was wrong. At this point, rdbuf()->in_avail() is returning 0 for newly opened istreams (that are not empty.). This is incorrect.
I suspect that the way to solve this is to set _M_buf and friends to real values instead of indeterminate values in filebuf's ctors. I did work up a partial solution to this based on this approach, but cannot find it at the moment.
Here's another testcase for this
#include <fstream>
#include <sstream>
#include <iostream>
void test01()
{
using namespace std;
streamsize sum = 0;
istringstream iss("shamma shamma");
// test01
size_t i = iss.rdbuf()->in_avail();
cout << i << endl;
// test02
size_t max = 0;
while (iss.good() && max < 10)
{
char buf[1024];
streamsize gotten = iss.readsome(buf, sizeof buf);
sum += gotten;
cout << gotten << " (" << sum << ")" << endl;
++max;
}
}
void test02()
{
using namespace std;
streamsize sum = 0;
ifstream ifs(__FILE__);
// test01
size_t i = ifs.rdbuf()->in_avail();
cout << i << endl;
// test02
size_t max = 0;
while (ifs.good() && max < 10)
{
char buf[1024];
streamsize gotten = ifs.readsome(buf, sizeof buf);
sum += gotten;
cout << gotten << " (" << sum << ")" << endl;
++max;
}
}
int main()
{
test01();
test02();
return 0;
}
http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=6746