Re: Commercial C To Ada 95 compiler

["SteveD" <nospam_steved94@attbi.com>]

"Jim Rogers" <jimmaureenrogers@worldnet.att.net> wrote in message
news:3D018106.6080004@worldnet.att.net...
> SteveD wrote:
>
[snip]
>
> You may be very wrong here. Ada compilers tend to identify many more
> errors at compile time than C compilers. This means that code
> which compiles without error on a C compiler, when directly translated
> to Ada, will may not compile.
>
> One simple example is indexing past the end of an array.
> C compilers simply will not catch this problem. Ada compilers will.

In fact this is not an error in C.  Programs can (and do) intentionally
index past the end of arrays.  I have seen C code that allocates memory
dynamically and uses array access to reference the memory.  It is nearly
impossible to distinguish these cases.

> On the whole, direct translation may not be possible. C uses
> implicit conversion between integer and floating point types.
> Ada provides no such implicit conversion. You will at least need
> to make all implicit C conversions explicit in Ada.

I disagree, direct translation is possible.  The order of conversions in C
is explicitly defined.  The translation would have to turn these implicit
conversions into explicit conversions.  Again, a review of the translated
could may reveal surprises.

> Another incompatibility is trying to reference the control
> variable in a "for" loop outside the scope of the "for" loop.
> This is impossible in Ada and not uncommon in C. The C compiler
> will allow this. The Ada compiler will not.

In this case a direct translation should translate the for loop to a while
construct.  For a direct translation the generated code must behave exactly
the same as the original code.

> Your example of "direct" translation of a C for loop with a null
> body to an Ada while loop is a good approximation of the problem,
> but not, IMHO, a direct translation. A direct translation would have
> the C code also using a while loop. Ada for loops simply cannot
> demonstrate this error. Any attempt to do so will create a
> compiler error.

You miss my point.  The translation is from C to Ada.  I can't change the C
code, I'm translating it.

In my example the C code had an error, the fact that the for loop was empty
was missed in the original code.  This shows up readily in the Ada code.

BTW:  I'm not saying I would want a C to Ada translator.  I'm just saying
that if someone said they wanted one, I can understand their reasoning.

SteveD

>
> Jim Rogers
>