🚀 go-pugleaf

In article <4l4ldb$nkl@srvr1.engin.umich.edu>
           hasdi@news-server.engin.umich.edu "HASDI RODZMANN HASHIM" writes:

>The way I understand it, type-conversion is to transform the bits of one
>variable so that it is representable as the type to be converted into. eg. 
>(int)my_float. type-casting doesn't transform the bits at all, but force
>the compiler to treat that variable as the specified type... which is
>highly unportable. Why would anyone want to typecast then? Can somebody
>clarify this for me? 

You've misunderstood. Casting is simply a way of forcing type conversions
explicitly - changes of representation i.e. the bits patterns or even the
number of bits occupied by the value are in general required. For example

    int i;
    double d;

    i = 1;

    x = i;

This involves an implicit conversion and the result will be that x contains
1.0 (or something as close as possible to it).

    x = (double) i;

has exactly the same result. However the conversion to double is performed
explicitly by the cast instead of implicitly by the assignment. Pointer
casts can also result in a change of representation for the pointer. However
there is no effect in what is being pointed to so you can end up with a
pointer pointing to something that was created as a different type. E.g.

    int x = 1;
    char *p = (char *)&x;

&x is a pointer to int which is cast to a pointer to char. The representation
of the pointer may change if the system uses different representations
fort int * and char * (some systems do). If you dereference p you will
be accessing what it points to as a char although the value containted in x
is represented as an int.


>As a side note, using typedef so that you can use "myrecord" instead of
>"struct myrecord_s" has been a real major bug to me.

Why? Structure tags allow you tag the fundamental structure types. typedefs
are a general mechanism in C to create aliases for any type including
structures.

>Unfortunately, this
>is necessary to avoid shift/reduce conflicts.

You may have to define the grammar differently but I see no need for
conflicts. The main issue is that in C tags have their own namespace. That
is only possible if they can be distinguished from other types of
identifier syntactically.

>Makes me wonder how C++ parser works.

There's nothing special here however C++ doesn't give tags a separate
namespace.

-- 
-----------------------------------------
Lawrence Kirby | fred@genesis.demon.co.uk
Wilts, England | 70734.126@compuserve.com
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