ANSI C++ Standard header files

In ANSI-C++ the way to include header files from the standard library has changed.

The standard specifies the following modification from the C way of including standard header files:

• Header file names no longer maintain the .h extension typical of the C language and of pre-standard C++ compilers, as in the case of stdio.h, stdlib.h, iostream.h, etc. This extension h simply disappears and files previously known as iostream.h become iostream (without .h).
• Header files that come from the C language now have to be preceded by a c character in order to distinguish them from the new C++ exclusive header files that have the same name. For example stdio.h becomes cstdio .
• All classes and functions defined in standard libraries are under the std namespace instead of being global. This not applies to C macros that remain as C macros.

Here you have a list of the standard C++ header files:

<algorithm>   <bitset>   <deque>   <exception>   <fstream>   <functional>   <iomanip>   <ios>   <iosfwd>   <iostream>   <istream>   <iterator>   <limits>   <list>   <locale>   <map>   <memory>   <new>   <numeric>   <ostream>   <queue>   <set>   <sstream>   <stack>   <stdexcept>   <streambuf>   <string>   <typeinfo>   <utility>   <valarray>   <vector>  

ANSI-C++	ANSI-C
<cassert>	<assert.h>
<cctype>	<ctype.h>
<cerrno>	<errno.h>
<cfloat>	<float.h>
<ciso646>	<iso646.h>
<climits>	<limits.h>
<clocale>	<locale.h>
<cmath>	<math.h>
<csetjmp>	<setjmp.h>
<csignal>	<signal.h>
<cstdarg>	<stdarg.h>
<cstddef>	<stddef.h>
<cstdio>	<stdio.h>
<cstdlib>	<stdlib.h>
<cstring>	<string.h>
<ctime>	<time.h>
<cwchar>	<wchar.h>
<cwtype>	<wtype.h>

Since now classes and functions of the standard libraries are located within the std namespace we must use the C++ using directive for that these become usable in the same way they were in pre-standard code. For example, to be able to use all the standard classes of iostream we would have to include something similar to this:

#include <iostream>
using namespace std;

#include <iostream.h>

Nevertheless for compatibility with ANSI-C, the use of name.h way to include C header files is allowed. Therefore, both following examples are valid and equivalent in a compiler which fulfills ANSI-C++ specifications:

// ANSI C++ example #include <cstdio> using namespace std; int main () { printf ("Hello World!"); return 0; }

// pre ANSI C++ example // also valid under ANSI C++, but deprecated #include <stdio.h> int main () { printf ("Hello World!"); return 0; }

In all the examples of the current version of The C++ tutorial it has been chosen to include the old way because to date is the most compatible format (and also shorter), although if you have a compiler that supports ANSI-C++ standard I recommended you the use of the new format in your programs.

©The C++ Resources Network, 2000 - All rights reserved

Return back Return to Documents section