Mail Archives: djgpp/1997/08/17/03:45:50
On Fri, 15 Aug 1997, Hans-Bernhard Broeker wrote:
> How much more time *does* it take for a rather small program, using,
> say the STL string classes compared to the same program using C string
> functions? Of course 8M is really not too much memory for gcc
> compiling C++ with some largish headers (I've seen it take 8M and more
> on Linux, using C++ X libraries and similar stuff), so you might want
> to just shell out the money to upgrade those boxes to 16 MB (or dump
> the -33 one completely and put its SIMMs into the -100 box :-)
The following file took 16 sec's ave. to compile (from the command line,
with gxx) with USE_CPP defined, and 10 sec's ave. to compile without.
The file was compiled to an object file, so link time is not a factor
(the times were the same anyway).
#ifdef USE_CPP
#include <iostream.h>
#else
#include <stdio.h>
#endif
int main()
{
#ifdef USE_CPP
cout << "This is a test of compile times.";
#else
printf( "This is a test of compile times." );
#endif
return 0;
}
The file is absurdly small enough that the 6 sec difference can only be
attributed to the size of the header file. While 6 sec's isn't a lot,
large template files like algo.h and vector.h take much longer. That time
is spent for each file to be compiled that includes algo.h and vector.h,
rather than just once, so it adds up. (I didn't try a test with algo.h
and vector.h, because there's nothing in the C library that, alone, would
give the same functionality. That's why STL is so nice.)
Furthermore, when the actual code file is more complicated, even though it
might only be 200 lines, the caches on my small machines with the slow
hard drives start to thrash and that 6 sec's multiplies to give waits of
more than a minute extra per file.
By the way, the 486-33 is the computer at work, the 486-100 is at home,
so dumping the 33's ram into the 100 isn't an option. As for shelling
out some money, I wish I had some to shell out. :)
> I don't think I understand your reasoning here: why do you think you
> need debugging *libraries* to use '-g' for gcc? I mean: you're not
> planning to routinely debug the standard C/C++ libraries themselves,
> are you? What prevents you from linking .o files compiled with '-g' to
> the stock libraries?
I don't think I explained this right, because I don't really understand
it. When I pass the -g option to gcc on the SGI it tells me something
like '-g not available in this configuration'. I didn't realize that not
having -g was a configurable option. Anyway, I said debugging libraries
because I didn't know how else to explain it. Either way, I can't debug
on the SGI, so I have to do it on the PC.
---------------
Peter Berdeklis
Dept. of Physics, Univ. of Toronto
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