Path: ...!news.mixmin.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Malcolm McLean <malcolm.arthur.mclean@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: Whaddaya think?
Date: Sun, 16 Jun 2024 17:17:52 +0100
Organization: A noiseless patient Spider
Lines: 60
Message-ID: <v4n37h$4goj$1@dont-email.me>
References: <666ded36$0$958$882e4bbb@reader.netnews.com>
 <v4n1nf$2fae$1@dont-email.me>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Injection-Date: Sun, 16 Jun 2024 18:17:53 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="89fd4fc902c96a94ecd3a3858c2eb313";
	logging-data="148243"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/Kl/zzIJQpeM5iw/+O5kV23zNiGcCC+5w="
User-Agent: Mozilla Thunderbird
Cancel-Lock: sha1:o0ly6h6goII3CJWenZdaLC6qGE0=
In-Reply-To: <v4n1nf$2fae$1@dont-email.me>
Content-Language: en-GB
Bytes: 3222

On 16/06/2024 16:52, Lew Pitcher wrote:
> On Sat, 15 Jun 2024 15:36:22 -0400, DFS wrote:
> 
>> I want to read numbers in from a file, say:
>>
>> 47 185 99 74 202 118 78 203 264 207 19 17 34 167 148 54 297 271 118 245
>> 294 188 140 134 251 188 236 160 48 189 228 94 74 27 168 275 144 245 178
>> 108 152 197 125 185 63 272 239 60 242 56 4 235 244 144 69 195 32 4 54 79
>> 193 282 173 267 8 40 241 152 285 119 259 136 15 83 21 78 55 259 137 297
>> 15 141 232 259 285 300 153 16 4 207 95 197 188 267 164 195 7 104 47 291
>>
>>
>> This code:
>> 1 opens the file
>> 2 fscanf thru the file to count the number of data points
>> 3 allocate memory
>> 4 rewind and fscanf again to add the data to the int array
>>
>>
>> Any issues with this method?
> 
> Others have (and will continue to) address this question.
> 
>> Any 'better' way?
> 
> Not so much "better", as "other".
> 
> ISTM that you waste an opportunity (and expose a common 'blind-spot')
> in your first loop:
> 
> Here,
>>   while(fscanf(datafile, "%d", &j) != EOF){
>>     N++;
>>   }
> you discard a lot of work (done for you by fscanf() to determine the
> value of each input number) just to be able to count the number of
> numbers in your input. What if there were a way to put this (to you)
> byproduct of fscanf() to use, and avoid using fscanf() entirely in
> the second pass?
> 
> You /could/ create a temporary, binary, file, and write the fscanf()'ed
> values to it as part of the first loop. Once the first loop completes,
> you rewind this temporary file, and load your integer array by reading
> the (now converted to native integer format) values from that file.
> 
> Still two passes, but using fscanf() in only one of those passes.
> 
> (BTW, the 'blind-spot' I mentioned is that we often forget that
> we /can/ use temporary files to store intermediary results. Sometimes
> we can manipulate a temporary file easier than we can manipulate
> malloc()ed (or other) storage. )
 >
Exactly. People complain that it is a hassle to realloc() a buffer.

So just use a temporary file.

-- 
Check out my hobby project.
http://malcolmmclean.github.io/babyxrc