bagpiper@oxy.edu (Michael Paul Hunter) (07/28/88)
I was reading the TurboC 1.5 manual on static and near functions and it seemed
to me that the two were synonomous except for the fact that I couldn't
deterimine if static generated near calles. So maybe one should
#define static as near static??????? (NOTE: I am not saying that near is
a good thing, but if static does what near does, but uses far calles one
might as well go all the way and yes, I know it is not portable....but then
if you use the #define mentioned above it would be easy [via conditional
compilation or even an editor job] to make it portable :))
Mike
Michael Hunter UUCP : ....{seismo, rutgers, ames}!cit-vax!oxy!bagpiper
Box 241 ARPA : bagpiper@oxy.edu
Occidental College
Los Angeles, CA 90041Howard_Reed_Johnson@cup.portal.com (08/03/88)
Someone asked a question about the difference between the 'static'
keyword and the 'near' keyword used in 80x86 compilers, viz.:
What's the difference between these declarations?
static int func() { return(0); }
static near int func() { return(0); }
Using static in this context (outside a function) simply means
that the symbol referred to is not visible outside that source file.
The near qualifier instructs the 80x86 compiler to expect to be
called with a near call (as opposed to a far call).
The two are not equivalent, since the address of 'func' can be
given to other program modules via a pointer to function:
int (*pfi)() = func;alvidrez@heathcliff (Jeff Alvidrez) (08/05/88)
In article <7836@cup.portal.com> Howard_Reed_Johnson@cup.portal.com writes: > >The near qualifier instructs the 80x86 compiler to expect to be >called with a near call (as opposed to a far call). > >The two are not equivalent, since the address of 'func' can be >given to other program modules via a pointer to function: > > int (*pfi)() = func; More significantly, the linker will fail with a segment fixup error if you compile in a large code model and try to call a near function from code in another source file. This is because the large models on most PC C compilers make a separate code segment for each source file (module) and saves space in the object code for a 32-bit (far) address for all function calls. A near function's object file information has only a 16-bit address, so the linker will throw its hands up in despair, and you will be left without an executable. It is a good thing that the linker fails here, however, because if it did not, the near function would use a near return, leaving the segment address of the far caller on the stack and returning to who knows where. I think prototypes help prevent such things, but of course you have to be disciplined enough to use them (yuk). MSC has a flag that generates them automatically, but in TC you just have to do it manually. This may have slightly different results on different compilers, but this is what happens in Turbo C. I believe most of this stuff is in the sections of the MSC/TC manuals on memory models. Codeview also helps a lot when you are in doubt; seeing the code a compiler generates and watching it in action can go a long way to understanding what these language constructs REALLY mean. It is unfortunate that we have to be concerned with these things, but blame that on IBM's use of a segment-addressing CPU; on most virtually addressed systems, people can go through life believing that C is a low-level language because it gets about as close to the underlying architecture as the average programmer needs to go. /jra PS To use Codeview with Turbo C you have to generate assembler source and proceed from there as if you were assembling (with Microsoft MASM) for Codeview. Not source level, but better than SYMDEB or printf(). When o when will we see Borland's AMAZING debugger? -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Jeff Alvidrez alvidrez@heathcliff.cs.columbia.edu The opinions expressed in this article are fictional. Any resemblence they may bear to real opinions (especially those of Columbia University) is purely coincidental. -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-