Buffer or Realloc?

Is it generally better to set-up a buffer (fixed sized array) and read
and write to that
buffer even if it is larger than what is being written to it? Or is it
better to allocate memory and realloc it for the size of the what is
being written each time? In other words, what is the decision factor
between deciding to use a fixed size buffer or allocating memory
space and reallocing the size?

I don't think the code below is optimal since the size of the "buffer"
becomes extremely small when I realloc it. I also spend time
re-allocating
it. And taking this to the next step, if I wrote to a linked list or a
red black
tree, I would have to allocate memory. In that case, how do I
determine
the best size?

Note: The code below contains some posix items. Please ignore those
items. I have also left out some error coding below as well.
The
below was written to just learn the regex API.

int
main(void) {

regex_t preg;
char *string = strdup("hello1hello4hello2hello3 are you hello");
char *match;
regmatch_t pmatch[1];
size_t nmatch = 1;
size_t len = 0;
size_t offset = 0;
int test;

match = calloc(BUFSIZ, sizeof(char));


if ( regcomp(&preg, "hello[41]", REG_BASIC) != 0)
perror("regcomp failed");

while (string[offset] != '\0') {
test = regexec((const regex_t *)&preg, &string[offset],
nmatch, pmatch,0);
if (test == REG_NOMATCH || test !=0) {
break;
}
len = pmatch[0].rm_eo-pmatch[0].rm_so;
/* is this optimal or should I use a fixed sized buffer? */
match = realloc(match, len+1);
strlcpy(match, &string[offset],
len+1);
(void)printf("matched string: %s\n", match);
offset += pmatch[0].rm_eo;

}
(void)printf("original string: %s\n", string);
free(match);
regfree(&preg);
exit(0);
}

.

Relevant Pages

  • Re: Buffer or Realloc?
    ... better to allocate memory and realloc it for the size of the what is ... between deciding to use a fixed size buffer or allocating memory ... Fixed size arrays are good for things that whose contents *CANNOT* ... becomes extremely small when I realloc it. ...
    (comp.lang.c)
  • Re: Buffer or Realloc?
    ... better to allocate memory and realloc it for the size of the what is ... between deciding to use a fixed size buffer or allocating memory ... becomes extremely small when I realloc it. ... I would have to allocate memory. ...
    (comp.lang.c)
  • Re: Buffer or Realloc?
    ... better to allocate memory and realloc it for the size of the what is ... between deciding to use a fixed size buffer or allocating memory ... so for the string I've got to prepare as part of a message to the UK Government gateway where the specification says the string has a maximum length of 10 characters I should not use a fixed size buffer but a reallocating buffer? ... with the realloc() approach -- obviously ...
    (comp.lang.c)
  • Re: Buffer or Realloc?
    ... better to allocate memory and realloc it for the size of the what is ... between deciding to use a fixed size buffer or allocating memory ... so for the string I've got to prepare as part of a message to the UK Government gateway where the specification says the string has a maximum length of 10 characters I should not use a fixed size buffer but a reallocating buffer? ... you only want to realloc more space if you need it. ...
    (comp.lang.c)
  • Re: Buffer or Realloc?
    ... # Is it generally better to set-up a buffer (fixed sized array) and read ... It's generally better to not overrun your buffer. ... Justice is dead. ...
    (comp.lang.c)