NetNews Usenet Archive 1992 #18/NN_1992_18.iso/spool/comp/lang/c/12251

Internet Message Format | 1992-08-12 | 2.1 KB

Path: sparky!uunet!mcsun!uknet!ox-prg!oxuniv!atmtjkv
From: [e-mail]
Newsgroups: comp.lang.c
Subject: Re: Allocate memory to typed in string, How?
Message-ID: <[e-mail]>
Date: 12 Aug 92 07:22:16 GMT
References: <[e-mail]> <[e-mail]> <[e-mail]>
Organization: Oxford University VAX 6620
Lines: 42

In article <[e-mail]>, [e-mail] (Murray Nesbitt) writes:
>
> In article <[e-mail]> [e-mail] (Bibhas Bhattacharya) writes:
>
>>I wrote a simple function to take care of any arbitrary length string
>>input.  It doesn't take any argument, returns a pointer to the string.
>>Here's how it might look in a program. Hope this helps someone new to
>>C like me.
>>
>
>>        scanf("%c",&temp);
>>        if(string == (char *)NULL)
>>            string=(char *) malloc(sizeof(char));
>>        else
>>            string = (char *) realloc(string, (numchar+1) *
>>                sizeof(char));
>
> You can do without the above conditional: just call realloc()
> unconditionally (as you've already initialized ``string'' to NULL, and
> with a NULL first argument realloc() behaves like malloc()).  The loop
> will run faster without the conditional.
>
> As well, you should check the return value of realloc(), and return
> NULL if there is a failure.
> Murray
> --
--
Faster than reallocing with one extra byte each time is to store the
number of bytes allocated separately, and then doubling it each time
the string length exceeds the allocated space.  This obviously
has a memory penalty, but reduces the number of system requests,
making the allocation go as log(string length) rather than (string length).
It's not worth it with very short strings, but the initial allocation
can be larger than 1 byte, if you can spare the memory.
(I use this technique in a plot driver for sunwindows, which stores each page
in a buffer to allow subsequent redisplay or filtering; the strings in that
case can be 8K long!)

Tim Kingsmill-Vellacott
Atmospheric, Oceanic and Planetary Physics
University of Oxford, UK.
[e-mail]  preferred