From: peuha AT cc DOT helsinki DOT fi (Esa A E Peuha)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Need help with DJGPP's "_dos_ds" macro
Date: 21 Jan 1997 13:27:32 GMT
Organization: University of Helsinki
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Graham Howard Wile (an118 AT chebucto DOT ns DOT ca) wrote:
: 	When I compile my test program, however, gcc gives my an error saying
: the "_dos_ds" function is undefined. I've included the library "farptr.h" and
: tried to compile a program with this line after having used Allegro to set
: my video mode to 13h:


: 		_farpokeb(_dos_ds, 0, 23);

: 	It says the "_dos_ds" function isn't defined.

: 	Also, the compiler won't let me link to the "farptr.h" library by
: putting "-lfarptr" switch on. It says it can't find the file "-lfarptr".
: It does this with other libraries I try to link this way too. But it will 
: let me link to "iostream.h" by putting a "-liostream" on the end of my 
: command line. Why does it do this, and not recognize the "_dos_ds" even
: though I've included "farptr.h" in my code ?

: 						Thanks very much
: 							Graham

The *.h files are not libraries. They are used to define function
prototypes, constant definitions, and the like. These files are used by
putting a line like `#include <XXX.h>´ in any source file which calls
the functions or uses the values defined in XXX.h. When the source file
is preprocessed, the preprocessor replaces any `#include <XXX.h>´ with
the contents of XXX.h in its output. Libraries, on the other hand, are
the `lib*.a´ files in the lib/ subdirectory. They are (usually)
compressed collections of object files, which contain the code of the
library functions. Libraries are used by invoking the compiler (or
linker) with `-lXXX´ switch, which causes the linker to search file
`libXXX.a´ for functions that should be linked within the program.
Normally, there is no one-to-one correspondence between include files
and libraries in standard C (this is not true in C++; the class
libraries often have their own inclue files). The `_dos_ds´ macro in not
defined in `farptr.h´ but in (if I remember correctly) `go32.h´; putting
line `#include <go32.h>´ should solve your problem.

--
Esa Peuha
student of mathematics at the University of Helsinki
http://www.helsinki.fi/~peuha/