Passing ifstream as an argument to Class Constructor

Question

I am trying to pass: ifstream infile;

in my main (), to the constructor of a class called "FIFO": FIFO (infile);

In the header file of FIFO (FIFO.h), I have:

FIFO (std::ifstream);
std::ifstream infile;

And in FIFO.cc, I have:

FIFO::FIFO (std::ifstream & INFILE)
{
         infile = INFILE;
}

I kept getting like (There are more of them, I just paste one of them):

In file included from /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/localefwd.h:43, from /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/string:45, from FIFO.cc:7: /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/ios_base.h: In member function ‘std::basic_ios >& std::basic_ios >::operator=(const std::basic_ios >&)’: /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/bits/ios_base.h:793: error: ‘std::ios_base& std::ios_base::operator=(const std::ios_base&)’ is private /usr/lib/gcc/x86_64-redhat-linux/4.4.7/../../../../include/c++/4.4.7/iosfwd:47: error: within this context

I am not sure if passing ifstream using reference works or not, or it is my codes problem.

Thanks!

It's best and common practice to avoid all-uppercase identifiers like FIFO and INFILE unless they're preprocessor macros... just helps avoid clashes and contain the "evils" of macros (see Marshall's C++ FAQ Lite if you're unaware of the issues). — Tony Delroy

Captain Obvlious Captain Obvlious · Accepted Answer · 2013-04-19T02:12:30

In your constructors declaration you are taking the std::ifstream by value instead of by reference. Instead of

FIFO (std::ifstream);

it should be

FIFO (std::ifstream&);

and you are storing the member variable 'infile' by value instead of by reference.

std::ifstream infile;

should be

std::ifstream& infile;

Since you are now storing a reference to the ifstream you need to initialize it in the initializer list instead of assigning it in the constructor.

FIFO::FIFO (std::ifstream & INFILE)
    : infile(INFILE)
{
}

This is because the copy constructor of std::ifstream is private (or deleted in C++11). By storing the member variable by value you are attempting to make a copy of the std::ifstream object passed to the constructor.

Passing ifstream as an argument to Class Constructor

2 Answers