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In article s2p@stellar.comnet.com, Bret Pehrson <BretP@strata3d.com> writes:
>I have noticed that the new C++ standard library headers do 
>not include the traditional '.h' extension.
>
>Does anyone have any insight as to why this is?

Many early C++ implementations used a file extension other than ".h" for
header files. Choices included ".H", ".hpp", ".hxx", ".h++", and perhaps
others. Looking at this problem in 1991, the C++ committee concluded that
enshrining ".h" in the standard would be seen as discriminating against
many implementations.

It is the rule in Standard C that the names of the standard headers used
in angle brackets need not correspond to the name of any file. That is,
when you write <stdio.h>, there need not be any file in the system with
the name "stdio.h". The implementation is free to map the reserved
header name (in angle brackets) to anything -- it need not be a file
at all, for example, but instead the reserved header names could simply
enable declarations predefined inside the compiler. Or the implementation
could map <stdio.h> to a file called "asdfghjkl" if it wished.

The C++ committee decided in 1991 to make this point more obvious by
eliminating the ".h" from the C++ standard header names, thus
discriminating equally against all implementations. :-)  Now you write,
for example, <iostream>, and you might wind up getting a header file whose
name is iostream.h, iostream.H, iostream.hpp, iostream.hxx, iostream.h++,
or "zxcvbnm". (Or perhaps the implementation doesn't use actual files.)

For compatibility, I would expect implementations to continue to accept
the same spelling of standard headers that they always accepted. Thus,
if a compiler previous used <iostream.hxx>, I would expect it to continue
to accept <iostream.hxx>, and pick up the same header file as <iostream>.

---
Steve Clamage, stephen.clamage@eng.sun.com



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>>>>> "SC" == Steve Clamage <clamage@Eng.Sun.COM> writes:

 SC> if a compiler previous used <iostream.hxx>, I would expect it to continue
 SC> to accept <iostream.hxx>, and pick up the same header file as <iostream>.

Wasn't there some rule about `#include <foo>' being treated like `#include
<foo.hxx>' followed by a bunch of `using' declarations?

Michael.
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Michael Cook <mcook@cognex.com> writes:

>>>>>> "SC" == Steve Clamage <clamage@Eng.Sun.COM> writes:

> SC> if a compiler previous used <iostream.hxx>, I would expect it to continue
> SC> to accept <iostream.hxx>, and pick up the same header file as <iostream>.

>Wasn't there some rule about `#include <foo>' being treated like `#include
><foo.hxx>' followed by a bunch of `using' declarations?

No. You are probably thinking of the two forms of the headers which
are inherited from Standard C. For example,
	<stdlib.h> and <cstdlib>
	<stdio.h>  and <cstdio>
	<string.h> and <cstring>
	... etc ...
The <cxxx> form corresponding to <xxx.h> puts all the declarations in
the "std" namespace. The <xxx.h> form, the form used in C, has those
same declarations in "std" followed by using-declarations for each
item. Thus, when you include <stdio.h>, the effect on the program
is the same as in a C program. If instead you include <cstdio>,
you can select the declarations you want by qualifying them explicitly
or by employing individual using-declarations, or you could get all
of them via a "using namespace std" directive.

The standard headers specific to C++ have only one form defined in
the standard, such as <new>, <iostream>, and so on. An implementation
can supply whatever additional headers it likes, with whatever
semantics it likes.
--
Steve Clamage, stephen.clamage@eng.sun.com


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