How to read string out of file with pointer?

[Xinyi Yang]

Hi,

I have to read information out of a file. The format will be
string1,string2 ,...,
string3,string4 ,...,
....
(the string sould not contain ' ' anyway)
the size of each string is uncertain. I plan to create an array to contain the pointers to the strings. Yet I don't know how to read a string out from the file any let a pointer point to it. I thought about using char *p=(int *) (malloc(n*(size of(char)))), but it means I have to first read the string to get the length, then read again and save it to the array. Is there any better way?
I would not like to use array with certain length since I don't know how long could a string be.

Thanks in advance!

Xinyi

[John Bode]

jo*******@my-deja.com (John Bode) wrote in message news:<43******* *************** ****@posting.go ogle.com>...

Xinyi Yang <ic***@slds1.de .lucent.com> wrote in message news:<3F******* ********@slds1. de.lucent.com>. ..

Hi,

I have to read information out of a file. The format will be
string1,string2 ,...,
string3,string4 ,...,
...
(the string sould not contain ' ' anyway)
the size of each string is uncertain. I plan to create an array to contain the pointers to the strings. Yet I don't know how to read a string out from the file any let a pointer point to it. I thought about using char *p=(int *) (malloc(n*(size of(char)))), but it means I have to first read the string to get the length, then read again and save it to the array. Is there any better way?
I would not like to use array with certain length since I don't know how long could a string be.

Thanks in advance!

Xinyi
The way I'd attack this is to create a dynamic buffer of size X using
malloc(), then reading a single character at a time into the dynamic
buffer, extending it as necessary using realloc(), until you see
either a ',' or EOF.

Quick, dirty, untested example:

#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>

#define START_SIZE 20 /* Initial buffer size */
#define EXTENT 5 /* Size to extend buffer by */

char *nextToken (FILE *in)
{
char *tmp, *p;
int phys_size = START_SIZE, cur_size = 0;
int nextchar;

/*
** Note: Do not cast the return value of malloc() unless
** you are using a pre-C89 compiler.
*/
p = malloc (START_SIZE);

if (p)
{
/*
** consume any leading whitespace
*/
while (isspace(nextch ar = fgetc (in))

) /* oops */ /* empty loop */;

while (nextchar != ',' && nextchar != EOF)
{
if (cur_size == phys_size - 1)
{
/*
** We've hit the end of the buffer.
** Use realloc() to extend it by
** EXTENT characters. For this example,
** a realloc() failure is a fatal error
** and we exit the program immediately.
** With a little effort you could make
** this handle such an error more gracefully.
*/
tmp = realloc (p, phys_size + EXTENT);
if (!tmp)
{
fprintf (stderr, "Buffer extend failed! Fatal
error!\n");
fflush (stderr);
exit (0);
}
phys_size += EXTENT;
p = tmp;
}
p[cur_size++] = c; p[cur_size++] = nextchar; /* oops^2 */

nextchar = fgetc (in); /* oops^3 */ }
p[cur_size] = 0; /* terminate the string */
}

return p;
}