Converting string from text file into numbers [duplicate]

Question

I have some difficulty in working with files in C. I already know how to read and write files in C but all I can do is just read and append. If I want to read lines of strings and converting them to numbers (int), how would I do it?

for example:

mytextfile.txt contains these data:

12345 30 15
 2111  9 20
  321 17  7

now for each line, I want to use the first number as a variable for price and the next number as quantity and the last number as discount. My problem is how am I going to store the three number on a variable so that I can use them as integers (or string)?

My output should have been the computed amount based on the price, quantity and discount listed down one value(the result) per line...

The fscanf function doesn't work for you? What else have you tried? Please read about how to ask good questions, and learn how to create a Minimal, Complete, and Verifiable Example. — Some programmer dude
– Some programmer dude, Commented Aug 19, 2016 at 12:03
I would read line by line and then use sscanf(linebuf, "%d%d%d", &price, &quantity, &discount); to get the numbers. — Klas Lindbäck
– Klas Lindbäck, Commented Aug 19, 2016 at 12:12

lost_in_the_source · Accepted Answer · 2016-08-19 12:47:56Z

0

#define MAXLINE 80

typedef struct {
    double cost, qty, disc;
} item;

int readitem(FILE *fp, item *itm)
{
    char buf[MAXLINE];

    if (fgets(buf, MAXLINE, fp) == NULL)
        return 0;

    return sscanf(buf, "%lf%lf%lf", &itm->cost, &itm->qty, &itm->disc);
}

The readitem function would get the next record, and read it into the itm pointer. You can call the function in a loop to get all the items:

#define MAXITEMS    255

item arr[MAXITEMS];
size_t i;
FILE *fin;

for (i = 0; i < MAXITEMS && readitem(fin, arr + i); ++i)
    ;

answered Aug 19, 2016 at 12:47

lost_in_the_source

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1 Comment

Kimba Over a year ago

Thanks a lot... i really have a lot to learn when it comes to C programming... it is old and difficult yet challenging...

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