#260 ifstream doesn't clear the failbit flag when open file, which violate the C++ standard, and cause confusing behavior of the user application.

[wuzijing]

Description: ifstream doesn't clear the failbit flag when open file, which violate the C++ standard, and cause confusing behavior of the user application.

Detail:
This bug is find in Android development environment, which have stlport 5.0 in it. And I also reviewed the code in latest released version 5.2.1 which should also have this issue.

REPRODUCE EXAMPLE:

std::ifstream sequenceFile(/*file path not exist*/ "/mnt/sdcard/test1.txt");
if (sequenceFile.is_open())
{
    sequenceFile.open(/*file path existing*/ "/mnt/sdcard/test2.txt");
}
while (!sequenceFile.iseof()) // this will got infinite loop.
{
    std::string line;
    getLine(sequenceFile, line);
}

RELATED SOURCE CODE: (from _fstream.h)

505   void open(const char* __s, ios_base::openmode __mod = ios_base::in) {
506     if (!this->rdbuf()->open(__s, __mod | ios_base::in)) // <---------if failed, doesn't call this->clear()
507       this->setstate(ios_base::failbit);
508   }

OPERATIONAL ENVIRONMENT:
Android developer environment.

COMPILER VERSION:
g++ (GCC) 4.8

STLPORT VERSION
5.0 and 5.2

[Petr Ovtchenkov]

Looks you mean something like this:

std::ifstream sequenceFile( "nonexistent_file");
if ( !sequenceFile.is_open() ) {
  sequenceFile.open( "existent_file" ); // expected clear state word
  assert( sequenceFile.good() == true );
}

In part of "which violate the C++ standard" message looks not correct too.

The same opinion here: http://www.cplusplus.com/reference/fstream/ifstream/open/

<snip>
The function clears the stream's state flags on success (setting them to goodbit). In case of failure, failbit is set.
</snip>

But is any reference to STANDARD or DRAFT that say the same? I don't see.

Opposite opinion is here: https://groups.google.com/forum/#!topic/comp.lang.c++/ajqpgwCS0UU

(in case of fail use .clear() explicitly).

But nevertheless, at least it is reasonable about clear error state if open was successful...