Problem scanning a string from a text file into an array

Question

Let's say I have a simple words.txt file that has contents like this:

house
car
horse

So I want to scan those words into an array so it would be words[0] would be house, words[1] would be car etc.. So I am having this problem that it seems I am having an infinite while loop, why is that? And am I scanning the words properly?

#include <stdio.h>
#include <stdlib.h>
#define MAX_WORDS 10

int main() {
    FILE *f;
    f = fopen("words.txt", "r");
    char words[MAX_WORDS];
    int i = 0;
    while(1) {
        fscanf(f, "%s", &words[i]);
        if(feof(f)) {
            break;
        }
        i++;
    }
    fclose(f);
    return 0;
}

&words[i] can hold only one character! Maybe you want array of arrays? — anurag
– anurag, Commented Jan 21, 2021 at 13:07

alex01011 · Accepted Answer · 2021-01-21 13:32:06Z

2

Your array can hold 1 word or n series of characters. What you want is an array of strings. First dimension must have MAX_WORD size and 2nd MAX_WORD_LEN size.

#include <stdio.h>
#include <stdlib.h>
#define MAX_WORDS 10
#define MAX_LEN 51

int main() {
    FILE *f;
    f = fopen("words.txt", "r");
    char words[MAX_WORDS][MAX_LEN]; /* Can hold MAX_WORDS string of MAX_LEN chars */
    int i = 0;
    while(1) {
        fscanf(f, "%50s", words[i]);
        if(feof(f) || i == MAX_WORDS - 1) {
            break;
        }
        i++;
    }
    fclose(f);
    return 0;
}

edited Jan 21, 2021 at 13:32

answered Jan 21, 2021 at 13:14

alex01011

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1 Comment

Aldomond Over a year ago

Thank you, didn't know it was that simple

cmdLP · Accepted Answer · 2021-01-21 13:20:39Z

2

First, you should think about the array storing the strings. Remember that strings are arrays by them selves. When you know the maximal length of the words it is easy to define this array of char arrays:

#define MAX_WORD_LEN 32

char words[MAX_WORDS][MAX_WORD_LEN];

Then you can read each string like this

fscanf(f, "%s", words[i]);

Note: your code can lead to buffer overflows, because you do not have a check for the variable i and "%s" is considered insecure (like gets), because it assumes that the read string fits into the buffer. Do not use these if possible, otherwise use these only, when you trust the input: Never: ~~scanf("%s", ...);~~ or ~~gets(...)~~

If you know the width, you can use it with scanf as the following:

char str[11];
scanf("%10s", str); // one less than the buffer size

edited Jan 21, 2021 at 13:20

answered Jan 21, 2021 at 13:18

cmdLP

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2 Comments

cmdLP Over a year ago

@costaparas Right. But it would have worked, because it leads to the same address, but another type: instead of char[] (cast to char*) it would have been char(*)[], because on almost all plattforms the pointer to an array contains the same address as a pointer to the first element to that array.

costaparas Over a year ago

The typo I was referring to was &words[i] should've been words[i] (now corrected). The former would give a compiler error, so it wouldn't of "worked".

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