[boost] Re: Stdint header?

From: Greg Colvin (gcolvin_at_[hidden])
Date: 1999-07-28 21:02:11

From: Beman Dawes <beman_at_[hidden]>
> At 07:03 PM 7/28/99 -0600, Greg Colvin wrote:
> 
> >> Hum... This might be a problem in theory, but in practice are there
> >> really any compilers out there that would prevent (2)?  Anyone know
> >> of a real-world compiler with either of these limitations?
> >
> >I don't know about the real world (:-) but the standard seems to
> >say you should use the "name" form for including files.
> 
> I have read paragraphs 2 and 3 several times and can't see any
> difference, other that the ordering of sentances and "..." falling
> back to <...>.  Oddly enough, the only problem I ever had with a real
> compiler was with "..." although that was clearly a compiler bug.
> 
> What are you seeing that I am missing?

Not much, that's why I said "seems to".  We took these paragraphs
verbatim from the C standard, and the rational says, in effect,
"we wanted to say what these mean but couldn't" so its all pretty
much implementation defined.  I had thought that the intent was
that:
   <name> forms were intended for standard and system C++ headers;
   <name.h> forms were intended for standard and system C headers;
   "whatever" forms were intended for user source files;
where "headers" need not be files at all.

In the real world the main difference is how and where to search.

So for GCC we have:

   -Idir 
   Add the directory dir to the head of the list of directories to be 
   searched for header files. This can be used to override a system 
   header file, substituting your own version, since these 
   directories are searched before the system header file 
   directories. If you use more than one `-I' option, the directories 
   are scanned in left-to-right order; the standard system 
   directories come after. 

   -I- 
   Any directories you specify with `-I' options before the `-I-' 
   option are searched only for the case of `#include "file"'; they 
   are not searched for `#include <file>'. If additional directories 
   are specified with `-I' options after the `-I-', these directories 
   are searched for all `#include' directives. (Ordinarily all `-I' 
   directories are used this way.) In addition, the `-I-' option 
   inhibits the use of the current directory (where the current input 
   file came from) as the first search directory for `#include 
   "file"'. There is no way to override this effect of `-I-'. With 
   `-I.' you can specify searching the directory which was current when 
   the compiler was invoked. That is not exactly the same as what the 
   preprocessor does by default, but it is often satisfactory. `-I-' 
   does not inhibit the use of the standard system directories for 
   header files. Thus, `-I-' and `-nostdinc' are independent.

And for VC++ we have:

   #include "path-spec"

   #include <path-spec>

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

   Both syntax forms cause replacement of that directive by the entire 
   contents of the specified include file. The difference between the two 
   forms is the order in which the preprocessor searches for header files 
   when the path is incompletely specified.
 
   Quoted form
      This form instructs the preprocessor to look for include files in the 
      same directory of the file that contains the #include statement, and 
      then in the directories of whatever files that include (#include) that 
      file. The preprocessor then searches along the path specified by the /I 
      compiler option, then along paths specified by the INCLUDE environment 
      variable.
 
   Angle-bracket form
      This form instructs the preprocessor to search for include files first 
      along the path specified by the /I compiler option, then along the path 
      specified by the INCLUDE environment variable.