🚀 go-pugleaf

In article t78@inferno.mpx.com.au, msmith@jolt.mpx.com.au (Michael Smith) writes:
>Life is hard... and then you die. (Ronald.Tschalaer@psi.ch) wrote:
>: Morgan Herrington wrote:
>: > 
>: > Daniel Wood <dwood> writes:
>: > 
>: > > The following:
>: > >       ((char *)src)++;        /* src is an (int *) */
>
>
>I **THINK** that this was considered legal using K&R1 style C.

K&R1 said that a cast yielded a value, not an lvalue. The PCC compiler
did not check for this violation, and the code it generated happened
to do what the programmer intended. A generation of programmers grew
up thinking the code was valid, since compilers didn't complain and
the code worked.

I don't know what would have happened if the programmer wrote
	float f;
	(double)f = 10.0; /* will the compiler complain? */
	long l;
	(short)l = 5; /* how about this? */

Some compilers (including some I worked on) detected the error of trying
to use the result of a cast as an lvalue. Complaints from users about
how the compilers broke their code and they didn't care what ANSI said
resulted in the compilers allowing the code anyway -- at least in
non-strict mode.

>  It's not 
>legal as ANSI C but many compilers let you get away with it.  When you've 
>got 2000 or so lines of poorly documented spagetti code using such 
>constructs and the code works flawlessly then it is a tough decision to 
>order a re-write.

Yes. If you want to sell compilers, you have to make reasonable compromises
to keep customers happy.

>When 64KB was a lot of memory, an XT was fast and a Vax 11/750 was a 
>monster, people used to write some ugly code.  These days we can afford a 
>few extra bytes to make code readable.

What's interesting is that you can get the same effect with valid code
that should generate the same object code as the invalid original.
For example, instead of 
	((char*)src)++;
you can write
	(*(char**)(&src))++;
I don't claim this code is more readable, but you could encapsulate the
ugliness in a macro. For example:
	#define increment_as(ptr, T) ((*(T*)(&ptr))++)
	increment_as(src, char*);
---
Steve Clamage, stephen.clamage@eng.sun.com