如何在C和/或C ++中包含文件

Question

I have a header file that I am trying to include from another source file using include pre-processor directory. I have tried to use both quoted form as well as angle-braket form, but neither seem to do the job.

The file name is .>"hello.h and a directory where it is searched by the compiler. I have tried to include it like this:

• #include <.>"hello.h>
• #include <.\\>"hello.h>
• #include <.\\>\\"hello.h>
• #include ".>"hello.h"
• #include ".>\\"hello.h"

I also tried different C and C++ compilers — clang, gcc, clang++ and g++.

Obviously, none of the above worked or otherwise there would have been no question.

I thought that maybe the name is not legal according to the standard. Unfortunately, I have neither C nor C++ standard specifications on hand. The only authoritative source of information I could find was this MSDN page about #include directive, and GNU C preprocessor documentation, here . GNU's documentation does not say much, MSDN has the following clause, however:

The path-spec is a file name optionally preceded by a directory specification. The file name must name an existing file. The syntax of the path-spec depends on the operating system on which the program is compiled.

I am curious as to what C and C++ standards say about this?

Where do I find those OS-specific rules for C and C++ header file naming requirements? I am particularly interested in OS X, Linux and FreeBSD.

Why escaping < and/or " characters does not work?

How do I include my file?

Answer 1

I think you are out of luck with that file name from the draft C99 standard section 6.4.7 Header names the grammar is as follows:

header-name:
  < h-char-sequence >
  " q-char-sequence "
h-char-sequence:
  h-char
  h-char-sequence h-char
h-char:
    any member of the source character set except
    the new-line character and >
q-char-sequence:
  q-char
  q-char-sequence q-char
q-char:
    any member of the source character set except
    the new-line character and "

You have both a " and > in the file name which excludes you from both the q-char and h-char specification. I don't think you have much choice but to change the file name.

The grammar is the same in the draft C++ standard , section 2.9 Header names .

Answer 2

In both C and C++, that's not a valid header name since it contains both > and " .

The syntax for header names allows those delimited by <> to contain "any member of the source character set except new-line and > ", and those delimited by "" to contain "any member of the source character set except new-line and " ". There is no concept of an escape sequence.

Answer 3

" and > are not valid characters for a filename in Windows. Your filename should be hello.h, or .\\hello.h, or ..\\hello.h, but not .>"hello.h.

#include "hello.h"
#include ".\hello.h"
#include "..\hello.h"
#include "c:/temp/hello.h"

Which is why you will not find anything in MSDN about it.

ext3 allows most characters (several have to be escaped when used), but it is HIGHLY recommended that you do not use them when naming your header and source files (if for no other reason than readability). For more information: http://pic.dhe.ibm.com/infocenter/compbg/v121v141/index.jsp?topic=%2Fcom.ibm.xlcpp121.bg.doc%2Flanguage_ref%2Fc99preprocessor.html

Answer 4

What is an acceptable filename is implementation defined. I would have expected #include ".>\\"hello.h" to work, at least on systems where '>' and '"'` are legal in filenames, but there's no requirement that it work, and there are clearly systems where it won't, because such names are not legal in the system.

You might try forcing the issue:

#define NAME ".>\"hello.h"
#include NAME

But for practical purposes, you should limit your filenames to alphanumerics, underscores, and maybe hyphens (but I'd be leary of those as well). And with only one dot, before the extension. If you go looking for trouble, don't be surprised if you find it.

Which, of course, answers your last question: how do I include the file. You rename it to something sensible.