Convert ifstream to istream

Question

How would one go about casting a ifstream into a istream. I figure since ifstream is a child of istream I should be able to do so but I have been having problems with such a

Answer 1

Try:

std::ifstream* myStream;
std::istream* myOtherStream = static_cast<std::istream*>(myStream);
myOtherStream = myStream;   // implicit cast since types are related.

The same works if you have a reference (&) to the stream type as well. static_cast is preferred in this case as the cast is done at compile-time, allowing the compiler to report an error if the cast is not possible (i.e. istream were not a base type of ifstream).

Additionally, and you probably already know this, you can pass a pointer/reference to an ifstream to any function accepting a pointer/reference to a istream. For example, the following is allowed by the language:

void processStream(const std::istream& stream);

std::ifstream* myStream;
processStream(*myStream);

Answer 2

std::istream *istreamObj = dynamic_cast<std::istream *>(&ifStreamObj)

Answer 3

No cast is necessary.

#include <fstream>
int main()
{
    using namespace std;
    ifstream    f;
    istream&    s   = f;
}