i/o question

[Doug Harvey]

Hi there. Just trying to figure out how to do something in c++

In "C", I would typically do something like this

FILE *inp = stdin; /* default to stdin *

if (input_file
inp = fopen(input_file)

/* ... *

I tried doing something like this in C++, but couldn't get anything t
compile
ifstream inp = &cin

but no go

Any suggestions would be appreciated, in addition to comments abou
whether there is a more appropriate way to do this in c++
dou

--

 

[David White]

Hi there. Just trying to figure out how to do something in c++.

In "C", I would typically do something like this:

FILE *inp = stdin; /* default to stdin */

In C stdin is a FILE*.

if (input_file)
inp = fopen(input_file);

/* ... */

I tried doing something like this in C++, but couldn't get anything to
compile:
ifstream inp = &cin;

In C++ cin is an istream, but not an ifstream. Nor is it a pointer. Try
this:
std::istream &inp = std::cin;

This makes inp a reference to the istream object cin, so you can use inp as
though it is cin.

DW

 

[hacker++]

In C stdin is a FILE*.

Try this:

std::ifstream file;
if(input_file)
{
file.open(input_file);
}

std::istream& inp = file.is_open() ? file : std::cin;

int a,b;

inp >> a >> b;