NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c-part2/13034

Internet Message Format | 1996-08-05 | 3.3 KB

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From: Lawrence Kirby <[e-mail]>
Newsgroups: comp.lang.c
Subject: Re: Settle a bet please
Date: Wed, 03 Apr 96 23:39:20 GMT
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In article <4jufbc$[e-mail]> [e-mail] "Tim Berens" writes:

>>>{
>>>    printf("size is: %d",sizeof("My Name"));
>>>}

>>Remember sizeof doesn't produce a result of type int, rather size_t which
>>is some implementation-dependent unsigned type.

>Do people participate in this newsgroup simply to show their smarts by
>desperately seeking nits to pick?

Not generally, as far as I can tell.

>Also, even though it is remotely possible that size_t is not the same
>size as an int and that the compiler may not automatically cast it to
>an int for the function call Or that the size of "My name" will exceed
>32K and size_t will be a 2 byte unsigned integer,

size_t can't be an int so %d can never be the correct format specifier to
use for it.

I've never come across a compiler which attempts to convert an argument in
a variable argument list to an appropriate type. The language has very
specific rules as to what a compiler should do with such an argument so
the compiler can perform such a conversion if it can detect with certainty
a case of undefined behaviour. That is possible in this case with a standard
library function but having done so the much better approach would be to
warn about the problem rather than bodge it. In fact a number of compilers
do this. So one of the problems with the code is that it simply won't
compile cleanly on some compilers (e.g. gcc with suitable options).

sizeof("My Name") is guaranteed to be 8 and representable as an int which is
why I cast to int in this case. In the general case the correct solution
is to use the %lu format specifier and cast to unsigned long.

> does it really matter in this example?

Yes, it is the difference between well written code that has a well defined
meaning from the language spec. and low maintenance and poorly written
code whose behaviour is undefined by the language and is a time bomb waiting
to go off.

comp.lang.c should ideally be a newsgroup where you can learn something about
the correct use of the C language. That means that bad usage should not go
unchallenged.

> Can you name a compiler where
>printf("size=%d",sizeof("My Name"));  will not properly display
>"size=8"?

Not offhand but that is not really important. What is important is whether
the code actually means anything or not. If you are building or porting large
project you have to be able to trust its individual components.

However I could easily envisage a 64 bit system where size_t is a 64 bit
unsigned long and int is 32 bit.  Possibly DOS compilers that implement a
huge memory model may have size_t 32 bits and int 16 bits.

--
-----------------------------------------
Lawrence Kirby | [e-mail]
Wilts, England | [e-mail]
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