`<iosfwd>`

Include the iostreams standard header <iosfwd> to declare forward references to several template classes used throughout iostreams. All such template classes are defined in other standard headers. You include this header explicitly only when you need one of the above declarations, but not its definition.

        // DECLARATIONS
typedef T1 streamoff;
typedef T2 streamsize;
typedef fpos streampos;

       // CLASSES
class char_traits;
class ios;
class streambuf;
class istream;
class ostream;
class stringbuf;
class istringstream;
class ostringstream;
class filebuf;
class ifstream;
class ofstream;
        // END OF DECLARATIONS

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