Put data from file to array in C

Question

here's my code.

#include <stdlib.h>
#include <stdio.h>

int main() {
    //Vars
    FILE *fp;
    char word[9999],
        *arrayOfWords[9999];
    int wordCount = 0, i;
    //Actions
    fp = fopen("data.txt", "r");
    if(fp != NULL) {
        while(!feof(fp)) {
            fscanf(fp, "%s", word);
            arrayOfWords[wordCount] = word;
            wordCount++;
        }
        for(i = 0; i < wordCount; i++) {
            printf("%s \n", arrayOfWords[i]);
        }
    puts("");
    } else {
        puts("Cannot read the file!");
    }
    return 0;
}

I am trying to read some data from a text file and store it into an array. Everything is fine while I'm in the loop, but when I get out of there, any value of any index in my array is filled with the last word of the file. Could anyone help me find out mistakes I am doing?

Data file:

Hello there, this is a new file.

Result:

file.
file.
file.
file.
file.
file.
file.
file.

Any help would be appreciated!

Ivaylo Strandjev · Accepted Answer · 2013-02-18 16:33:16Z

2

You need to allocate memory for each individual member of your array(using malloc or by giving a second dimension of the array and declaring it of type char instead of char*). What you do is similar to:

char *s;
scanf("%s", s);

And this can not work in C. In fact here you have UB(undefined behavior), because the pointer is not initialized.

EDIT: you get all the fields in the array to point to your array word instead, once you have read word you should allocate new memory for the string and then strcpy word into it.

edited Feb 18, 2013 at 16:33

answered Feb 18, 2013 at 16:21

Ivaylo Strandjev

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2 Comments

iNfas Over a year ago

I just realized I pasted the wrong piece of code. Edited. But I guess it's still the same. I just don't get why every index of array has the correct value while it's in the loop.

Ivaylo Strandjev Over a year ago

I have edited your answer and now I know why all the fields have the same value - they in fact all point to word and that also explains why they all store the last values read. Try it out - modify word and check that all values also change.

rioki · Accepted Answer · 2014-06-03 06:16:54Z

1

There are atleast 2 points of concern in your code. char word[9999], *arrayOfWords[9999]; defines arrayOfWords to be an array of 9999 char pointers. This is one point of concern.

Another point is arrayOfWords[wordCount] = word;. Here to store the newly read word, you need to allocate space as arrayOfWords is an array of pointers. Please find your modified code as below.

int main() {
//Vars
FILE *fp;
char arrayOfWords[30];
int wordCount = 0, i;
//Actions
fp = fopen("data.txt", "r");
if(fp != NULL) {
    while(!feof(fp)) {
        fscanf(fp, "%s", &arrayOfWords[wordCount]);
        wordCount++;
    }
    puts("");
    for(i = 0; i < (wordCount - 1); i++) {
        puts(arrayOfWords[i]);
    }
puts("");
} else {
    puts("Cannot read the file!");
}
return 0;
}

edited Jun 3, 2014 at 6:16

rioki

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answered Feb 18, 2013 at 16:32

Ganesh

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Comments

twalberg · Accepted Answer · 2013-02-18 16:32:36Z

0

This:

arrayOfWords[wordCount] = word;

does not copy the current word into separate storage, it merely assigns another pointer to point to the same piece of storage that word does. So you end up with an array of pointers to the same word array. You need to separately allocate memory for each word and copy the characters that make up each word (and the NULL terminator), rather than the pointer.

answered Feb 18, 2013 at 16:32

twalberg

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