Why can't g++ find iostream.h?
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.
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.
<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.
Another related issue that wasn't mentioned here, so I will include it for anyone's future reference, is from the command line the compiler needs the environment path variable updated to find the location of the c++ header files. In windows you can just update the path environment using the 'advanced system properties' GUI and add the location of the c++ include files. This will update the PATH environment variable in Windows cmd & Cygwin automatically upon restarting the shell.
To update your PATH from Linux or the Cygwin shell type... PATH=$PATH:/your_path_here Example:PATH=$PATH:/cygdrive/c/cygwin/lib/gcc/i686-pc-mingw32/4.7.3/include/c++ Also a good idea to add just the include directory as well: PATH=$PATH:/cygdrive/c/cygwin/lib/gcc/i686-pc-mingw32/4.7.3/include/ ...or check the proper directories for the location of your installation's include files, I recommend installing mingw for use with Cygwin, which is envoked with g++.
To install additional needed packages in Cygwin re-run the Cygwin install utility & check install from Internet to add packages from web repositories and add mingw-gcc-g++ & mingw-binutils. To compile: g++ hello.cpp -o hello
If using the gcc utility instead compile with the command: gcc hello.cpp -o hello -lstdc++ ... to get your executable.
As long as you have either gcc or mingw installed and the path to the c++ include files is in your path environment variable, the commands will work.