storing input from stdin into list - c

Question

I'm going to be getting input in the following format and I wish to store it into an arraylist or maybe even a linked list (whichever one is easier to implement):
3,5;6,7;8,9;11,4;
I want to be able to put the two numbers before the ; into a structure and store these. For example, I want 3,5 to be grouped together, and 6,7 to be grouped together.
I'm unsure as to how to read the input and obtain each pair and store it. The input I'm going to get can be fairly large (up to 60-70mB).
I have tried to use strtok() and strtol() however I just can't seem to get the correct implementation.
Any help would be great
EDIT:
What I have tried to do up til now is use this piece of code to read the input:
char[1000] remainder;
int first, second;
fp = fopen("C:\\file.txt", "r"); // Error check this, probably.
while (fgets(&remainder, 1000, fp) != null) { // Get a line.
while (sscanf(remainder, "%d,%d;%s", first, second, remainder) != null) {
// place first and second into a struct or something
}
}
I fixed the syntax errors in the code, but when I try and compile, it crashes.

Answer 1

With the addition of a single line, the same answer provides a robust and flexible solution to your problem. Take the time to understand what it does. It is not complicated at all, it is simply basic C. In order for you to do your conversion from string to int, you have 2 choices provided by libc, atoi (no error checking) and strtol (with error checking). Your only other alternative is to code a conversion by hand, which given your comments in both versions of this question, isn't what you are looking for.
The following is a good solution. Take the time to learn what it does. Regardless whether you use fgets or getline, the approach to the problem is the same. Let me know what your questions are:
/* read unliminted number of int values into array from stdin
(semicolon or comma separated values, pair every 2 values)
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#define NMAX 256
int main () {
char *ln = NULL; /* NULL forces getline to allocate */
size_t n = 0; /* max chars to read (0 - no limit) */
ssize_t nchr = 0; /* number of chars actually read */
int *numbers = NULL; /* array to hold numbers */
size_t nmax = NMAX; /* check for reallocation */
size_t idx = 0; /* numbers array index */
if (!(numbers = calloc (NMAX, sizeof *numbers))) {
fprintf (stderr, "error: memory allocation failed.");
return 1;
}
/* read each line from stdin - dynamicallly allocated */
while ((nchr = getline (&ln, &n, stdin)) != -1)
{
char *p = ln; /* pointer for use with strtol */
char *ep = NULL;
errno = 0;
while (errno == 0)
{
/* parse/convert each number on stdin */
numbers[idx] = strtol (p, &ep, 10);
/* note: overflow/underflow checks omitted */
/* if valid conversion to number */
if (errno == 0 && p != ep)
{
idx++; /* increment index */
if (!ep) break; /* check for end of str */
}
/* skip delimiters/move pointer to next digit */
while (*ep && (*ep <= '0' || *ep >= '9')) ep++;
if (*ep)
p = ep;
else
break;
/* reallocate numbers if idx = nmax */
if (idx == nmax)
{
int *tmp = realloc (numbers, 2 * nmax * sizeof *numbers);
if (!tmp) {
fprintf (stderr, "Error: struct reallocation failure.\n");
exit (EXIT_FAILURE);
}
numbers = tmp;
memset (numbers + nmax, 0, nmax * sizeof *numbers);
nmax *= 2;
}
}
}
/* free mem allocated by getline */
if (ln) free (ln);
/* show values stored in array */
size_t i = 0;
for (i = 0; i < idx; i++)
if ( i % 2 == 1 ) /* pair ever 2 values */
printf (" numbers[%2zu] numbers[%2zu] %d, %d\n", i-1, i, numbers[i-1], numbers[i]);
/* free mem allocated to numbers */
if (numbers) free (numbers);
return 0;
}
Output
$ echo "3,5;6,7;8,9;11,4;;" | ./bin/parsestdin2
numbers[ 0] numbers[ 1] 3, 5
numbers[ 2] numbers[ 3] 6, 7
numbers[ 4] numbers[ 5] 8, 11