Convert a set of chars to int from a file - c

Question

I'm reading:
22:5412:99:00 (...)
From a text file using (ch=fgetc(fp)) != EOF because I don't have only those numbers to read.
Identifying a number is easy with if(ch >= 48 && ch <= 57) but the thing is I want to put those numbers 22, 5412 into an array of integers. However when I read a char it reads part of number since each number is char.
It gets 2 (and not 22 like I want to) and in the next iteration reads the other 2. How can I save each set of numbers into it's own integer?
I hope I was clear enough, thanks!

Answer 1

My idea is to read in each char, and if it is a digit append it to a buffer. Whenever we get a non-digit, we just read the contents of the buffer as a string using sscanf, and clear the buffer for the next value.
#include <stdio.h>
#include <stdlib.h>
int read_buffer(char* buffer, int* sz)
{
int ret;
if (*sz==0) return 0;
buffer[*sz]='\0'; //end the string
sscanf(buffer,"%d", &ret); //read the contents into an int
*sz=0; // clear the buffer
return ret;
}
int main()
{
char buffer[1000];
int sz=0;
char ch;
FILE* input=fopen("input.txt","r");
// "input.txt" contains 22:5412:99:00
while ((ch=fgetc(input))!=EOF)
{
int number;
if (isdigit(ch))
{
buffer[sz++]=ch; // append to buffer
}
else
{
printf("Got %d\n",read_buffer(buffer,&sz)); // read contents of buffer and clear it
}
}
if (sz) // check if EOF occured while we were reading a number
printf("Got %d\n",read_buffer(buffer,&sz));
fclose(input);
return 0;
}

Answer 2

You would need to store the numbers as a string or a char* and use atoi to actually convert it to a number. http://www.cplusplus.com/reference/clibrary/cstdlib/atoi/

Answer 3

Assuming your pattern is of the type NN:NNNN:NN:NN, parse on the delimiter, feeding characters into a buffer:
int idx = 0, nIdx = 1;
int firstN, secondN, thirdN, fourthN;
char buf[5];
...
while ((ch=fgetc(fp)) != EOF) {
if (ch != ':') {
buf[idx++] = ch;
}
else {
buf[idx] = '\0';
idx = 0;
switch (nIdx++): {
case 1: firstN = atoi(buf); break;
case 2: secondN = atoi(buf); break;
case 3: thirdN = atoi(buf); break;
}
}
}
buf[idx] = '\0';
fourthN = atoi(buf);
...

Answer 4

I did a full program out of the previous post -- and some testing :-)
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
/* fill `array` with at most `siz` values read from the stream `fp` */
/* return the number of elements read */
size_t fillarray(int *array, size_t siz, FILE *fp) {
int ch;
size_t curr = 0;
int advance_index = 0;
while ((ch = fgetc(fp)) != EOF) {
if (isdigit((unsigned char)ch)) {
array[curr] *= 10;
array[curr] += ch - '0';
advance_index = 1;
} else {
if (advance_index) {
advance_index = 0;
curr++;
if (curr == siz) { /* array is full */
break;
}
}
}
}
return curr + advance_index;
}
int main(void) {
int array[1000] = {0};
int n, k;
n = fillarray(array, 1000, stdin);
if (n > 0) {
printf("%d values read:\n", n);
for (k=0; k<n; k++) {
printf(" %d", array[k]);
}
puts("");
} else {
fprintf(stderr, "no data read\n");
}
return 0;
}
And a test run
$ ./a.out
24555:76423 foobar 76235 jgfs(8) jhg x86-64 passw0rd RS232
[CTRL+D]
8 values read:
24555 76423 76235 8 86 64 0 232