ifstream from stdin

[Paulo da Silva]

How can I use a ifstream object to input from stdin?

Ex.
ifstream inf;
if (fn=="-")
{ what here to use inf as cin?
}
else
{ inf.open(fn.c_str,ios::in);
}
inf >> ...

Thanks.

 

[Robert Bauck Hamar]

How can I use a ifstream object to input from stdin?


Ex.
ifstream inf;

istream *inf;

if (fn=="-")
{ what here to use inf as cin?

inf = &cin;

}
else
{ inf.open(fn.c_str,ios::in);

inf = new ifstream(fn.c_str());

}
inf >> ...

*inf >> ...

....

if (inf == &cin)
delete inf;

 

[Kai-Uwe Bux]

istream *inf;


inf = &cin;


inf = new ifstream(fn.c_str());


*inf >> ...

...

if (inf == &cin)

Just a nit. I think, you want:

if ( inf != &cin )

delete inf;

Best

Kai-Uwe Bux

 

[Paulo da Silva]

Robert Bauck Hamar escreveu:

istream *inf;


inf = &cin;


inf = new ifstream(fn.c_str());


*inf >> ...

...

if (inf == &cin) !=
delete inf;

Thank you. This works ...

 

[James Kanze]

On some systems, opening "/dev/stdin" might work, but the general solution
is to use a pointer:

Or a reference.

istream *inf;

inf = &cin;

inf = new ifstream(fn.c_str());

*inf >> ...

if (inf == &cin)
delete inf;

More frequent, I think, is something along the lines of:

if ( argc == 1 ) {
process( std::cin ) ;
} else {
for ( int i = 1 ; i < argc ; ++ i ) {
std::ifstream in( argv[ i ] ) ;
if ( ! in ) {
std::cerr << "Could not open: " << argv[ i ] <<
std::endl ;
} else {
process( in ) ;
}
}
}

All the work is then done in "process( std::istream& )".