Why can't g++ find iostream.h?

Question

I'm trying to understand how to compile C++ programs from the command line using g++ and (eventually) Clang on Ubuntu.

I found a webpage which explains MakeFiles and I am following their directions. http://mrbook.org/tutorials/make/

I downloaded the four example files into their own directory.

• main.cpp
• hello.cpp
• factorial.cpp
• functions.h

I then went ahead and ran their example of how to manually compile without a MakeFile.

g++ main.cpp hello.cpp factorial.cpp -o hello 

When I ran the command from above, I received the following error from g++:

main.cpp:1:22: fatal error: iostream.h: No such file or directory compilation terminated. hello.cpp:1:22: fatal error: iostream.h: No such file or directory compilation terminated. 

My only experience with writing c++ is using an IDE such as VS C++ Express or CodeBlocks. Isn't the compiler supposed to know what iostream.h is and where to find it?

How do I get rid of this error so the program willl compile?

Thanks for any help.

Answer 1

Before the C++ language was standardized by the ISO, the header file was named <iostream.h>, but when the C++98 standard was released, it was renamed to just <iostream> (without the .h). Change the code to use #include <iostream> instead and it should compile.

You'll also need to add a using namespace std; statement to each source file (or prefix each reference to an iostream function/object with a std:: specifier), since namespaces did not exist in the pre-standardized C++. C++98 put the standard library functions and objects inside the std namespace.

Answer 2

<iostream.h> has never been a standard C++ header, because it did not make it into the C++ standard.

Instead we got <iostream>, in 1998.

Steer well clear of teaching material using non-standard stuff such as <iostream.h> or void main.

However, as a practical solution for your current pre-standard code, you may try to replace

#include <iostream.h> 

with

#include <iostream> using namespace std; 

It’s not guaranteed to work, but chances are that it will work.