I have this text sample
Ahmed 10
kmal 5
doola 6
And I am using this code to read it
if (myfile.is_open())
{
while ( myfile.good() )
{
myfile >> name;
myfile >> phone;
cout << name <<" "<<phone<<endl;
}
myfile.close();
}
I get this output
Ahmed 10
kmal 5
doola 6
doola 6
Why does this code read the last line twice ?
myfile.good() becomes false AFTER the read fails. Same with myfile.eof().
What you want is basically:
myfile >> name;
myfile >> phone;
if (!myfile.good()) break;
And this can be shortened to:
if (!(myfile >> name >> phone)) break;
or finally:
while (myfile >> name >> phone) { ... }
Try
while( myfile >> name >> phone ) {
// your code here
}
I believe the problem with the other approach is that eof isn't signaled until you actually try to read more than you should. That is, when you attempt to myfile >> name on the last round. That fails, as does myfile >> phone and only then do you break out of the loop.
Don't use while(myfile.good()). It will still say true, even when you have read the last line in your file. And then the next >> will fail, leaving the name and phone variables unchanged from the last input. Use this instead: while(myfile >> name >> phone) {...}
iostream status is not predictive. It reports the results of the previous operation, not of the next (which would be impossible to implement anyway). And myfile.good() isn't even a reliable indicator of the results of the previous operation: if the operation failed, it will be false, but if the operation succeeded, it's not necessarily true. Forget that function.
Use the fact that the stream can act as a boolean to test success of the previous operation. Once you have failure, you can then use eof(), and bad() to determine why (but with regards to eof(), only after failure---eof() may return true even if the previous operation succeeded). Thus:
while ( myfile >> name >> phone ) {
// ...
}
if ( myfile.bad() ) {
std::cerr << "Hardware read error" << std::endl;
} else if ( !myfile.eof() ) {
std::cerr << "Format error in file" << std::endl;
}
