Using and Porting GNU CC
Due to the differences between the filesystems of Unix and VMS, GNU CC
attempts to translate file names in `
#include' into names that VMS
will understand. The basic strategy is to prepend a prefix to the
specification of the include file, convert the whole filename to a VMS
filename, and then try to open the file. GNU CC tries various prefixes
one by one until one of them succeeds:
GNU_CC_INCLUDE:' logical name: this is where GNU C header files are traditionally stored. If you wish to store header files in non-standard locations, then you can assign the logical `
GNU_CC_INCLUDE' to be a search list, where each element of the list is suitable for use with a rooted logical.
SYS$SYSROOT:[SYSLIB.]'. This is where VAX-C header files are traditionally stored.
/' character), the preprocessor tries to convert it from Unix syntax to VMS syntax.
Conversion works like this: the first directory name becomes a device,
and the rest of the directories are converted into VMS-format directory
names. For example, the name `
translated to `
X11:foobar.h' or `
whichever one can be opened. This strategy allows you to assign a
logical name to point to the actual location of the header files.
Include directives of the form:
are a common source of incompatibility between VAX-C and GNU CC. VAX-C
treats this much like a standard
#include <foobar.h> directive.
That is incompatible with the ANSI C behavior implemented by GNU CC: to
expand the name
foobar as a macro. Macro expansion should
eventually yield one of the two standard formats for
#include "file" #include <file>
If you have this problem, the best solution is to modify the source to
#include directives to one of the two standard forms.
That will work with either compiler. If you want a quick and dirty fix,
define the file names as macros with the proper expansion, like this:
#define stdio <stdio.h>
This will work, as long as the name doesn't conflict with anything else in the program.
Another source of incompatibility is that VAX-C assumes that:
is actually asking for the file `
foobar.h'. GNU CC does not
make this assumption, and instead takes what you ask for literally;
it tries to read the file `
foobar'. The best way to avoid this
problem is to always specify the desired file extension in your include
GNU CC for VMS is distributed with a set of include files that is
sufficient to compile most general purpose programs. Even though the
GNU CC distribution does not contain header files to define constants
and structures for some VMS system-specific functions, there is no
reason why you cannot use GNU CC with any of these functions. You first
may have to generate or create header files, either by using the public
UNSDL (which can be found on a DECUS tape), or by
extracting the relevant modules from one of the system macro libraries,
and using an editor to construct a C header file.
#include file name cannot contain a DECNET node name. The
preprocessor reports an I/O error if you attempt to use a node name,
whether explicitly, or implicitly via a logical name.