CODEWITHSUNDEEP
c++io
Agrudge Amicus
Agrudge Amicus

Reputation: 1103

need for deriving iostream from istream and ostream

while studying I/O I came across:

iostream: istream reads from a stream, ostream writes to a stream, iostream reads and writes a stream: derived from istream and ostream

What is the need of inheritance if istream and ostream do the same job?

Upvotes: 0

Views: 301

Answers (2)

CSM
CSM

Reputation: 1272

The prototypes for a writer and reader are

class MyClass;
std::ostream& operator<< (std::ostream stream&, const MyClass &obj)
{
    obj->WriteTo(stream);
    return stream;
}

std::istream& operator>> (std::istream stream&, MyClass &obj)
{
    obj->ReadFrom(stream);
    return stream;
}

These functions (especially the writer) call lower-level stream functions on MyClass'es members.

Having std::iostream derived from both std::istream and std::ostream means that you can pass an instance of std::iostream to either function and it automatically pass in the correct part of std::iostream in.

std::istream and std::ostream are statically derived from std::ios which contains the common code for them.

Upvotes: 1

Werner Henze
Werner Henze

Reputation: 16726

Exactly by making iostream inherit from istream and from ostream you get a class that supports input and output and both interfaces (from istream and ostream). That doesn't mean that functionality is duplicated, it just means that the interfaces of istream and ostream and their implementation is being reused.

Upvotes: 1

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