# <iosfwd>

**[<iosfwd>](https://en.cppreference.com/w/cpp/header/iosfwd)** provides forward declarations of stream classes without including the full implementation. Use it in header files when you want to accept a stream parameter or return type without pulling in the heavy iostream headers.

It's a small optimization to reduce compile times.

## Example

This example declares a function that takes an ostream parameter using only forward declarations, avoiding the overhead of including iostream.

```cpp
// compile: g++ -std=c++11 -o iosfwdexample iosfwdexample.cpp
// run: ./iosfwdexample
// description: forward declaration of ostream in a header

#include <iosfwd>
#include <iostream>

void print_message(std::ostream& out);

void print_message(std::ostream& out) {
    out << "hello from iosfwd\n";
}

int main() {
    print_message(std::cout);
    return 0;
}
```