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From: David Brown <david.brown@hesbynett.no>
Newsgroups: comp.lang.c
Subject: Re: "undefined behavior"?
Date: Thu, 13 Jun 2024 15:21:54 +0200
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On 13/06/2024 00:34, DFS wrote:
> On 6/12/2024 6:22 PM, Keith Thompson wrote:
>> Janis Papanagnou <janis_papanagnou+ng@hotmail.com> writes:
>>> On 12.06.2024 22:47, DFS wrote:
>> [...]
>>>> before: char outliers[100];
>>>> after : char outliers[100] = "";
>> [...]
>>> Seriously; why do you expect [in C] a declaration to initialize that
>>> stack object? (There are other languages that do initializations as
>>> the language defines it, but C doesn't; it may help to learn before
>>> programming in any language?) And why do you think that "" would be
>>> an appropriate initialization (i.e. a single '\0' character) and not
>>> all 100 elements set to '\0'? (Someone else might want to access the
>>> element 'answer[99]'.) And should we pay for initializing 1000000000
>>> characters in case one declares an appropriate huge array?
>>
>> This:
>>      char outliers[100] = "";
>> initializes all 100 elements to zero.  So does this:
>>      char outliers[100] = { '\0' };
>> Any elements or members not specified in an initializer are set to zero.

Yes.  It's good to point that out, since people might assume that using 
a string literal here only initialises the bit covered by that string 
literal.

(In C23 you can also write "char outliers[100] = {};" to get all zeros.)

>>
>> If you want to set an array's 0th element to 0 and not waste time
>> initializing the rest, you can assign it separately:
>>      char outliers[100];
>>      outliers[0] = '\0';
>> or
>>      char outliers[100];
>>      strcpy(outliers, "");
>> though the overhead of the function call is likely to outweigh the
>> cost of initializing the array.

A good compiler will generate the same code for both cases - strcpy() is 
often inlined for such uses.

> 
> Thanks.  I'll have to remember these things.  I like to use char arrays.
> 
> The problem is I don't use C very often, so I don't develop muscle memory.
> 

What programming language do you usually use?  And why are you writing 
in C instead?  (Or do you simply not do much programming?)