reading int from file store first line in variables in c - c

Question

I am trying to read ints from a txt file and store the first line into three variable and the rest into an array.
while(fgets(lineBuf, sizeof(lineBuf), inputFile) != NULL){
fscanf(inputFile, "%d %d %d", &pages, &frames, &requests);
printf("\n\nin loop to get first line variables:\n Pages: %d\n frames: %d\n requests: %d", pages, frames, requests);
}
Input file: the numbers with the first row being the first three and every row afterwards just being a single number.
8 12 4
4
3
4
...
when i run the program, it skips the 12 and 4.

Answer 1

It skips because you are reading the file with fgets as well, so fgets get
the first line, fscanf the second line but leaves the newline in the input
buffer, so fgets will read only an empty line, etc. It's a bad idea to mix
both reading function.
The best thing would be to read all lines with fgets and parse each line with
sscanf. Use the return value of sscanf to determine how many integer you've
read. From your input it seems that a line can have 1, 2 or 3 integers. So this
would do:
char line[1024];
while(fgets(line, sizeof line, inputFile))
{
int pages, frames, requests, ret;
ret = sscanf(line, "%d %d %d", &pages, &frames, &requests);
if(ret < 1)
{
fprintf(stderr, "Error parsing the line, no numbers\n");
continue;
}
if(ret == 1)
{
// do something with pages
} else if(ret == 2) {
// do something with pages & frames
} else if(ret == 3) {
// do something with pages, frames and requests
}
}
edit
based on your comments, of only the first line has 3 values and the rest of the
lines have one value each, then you can simplify the code like this:
#include <stdio.h>
int parse_file(const char *fname, int *pages, int *frames, int *request, int *vals, size_t size)
{
size_t idx = 0;
if(fname == NULL || pages == NULL || frames == NULL
|| request == NULL || vals == NULL)
return -1;
FILE *fp = fopen(fname, "r");
if(fp == NULL)
{
fprintf(stderr, "Cannot open %s\n", fname);
return -1;
}
if(fscanf(fp, "%d %d %d", pages, frames, request) != 3)
{
fprintf(stderr, "Wrong format, expecting pages, frames and requests\n");
fclose(fp);
return -1;
}
// reading all other values and storing them in an array
while((idx < size) && (fscanf(fp, "%d", vals + idx) == 1)); // <-- note the semicolon
fclose(fp);
return idx; // returning the number of values of the array
}
int main(void)
{
int pages, frames, request, vals[100];
int num = parse_file("/your/file.txt", &pages, &frames, &request,
vals, sizeof vals / sizeof vals[0]);
if(num == -1)
{
fprintf(stderr, "Cannot parse file\n");
return 1;
}
// your code
return 0;
}