Problem with while loop when I read words from a file in C

Question

I am trying to create a program which :

1. finds the word with largest length from a file
2. creates a dynamically allocated 2d array
3. stores the words from the file to array

https://gist.github.com/up1047388/363854cbe703a6f297ebb644c50d307f (the whole program)

the file: https://gist.github.com/up1047388/758574c484d916c4aeba106f293f185a

The problem is in this loop (I used printf as a hint to find the problem but the program does not print anything inside the problem):

That's I am trying to do in the loop is the following :

1. pass the character which has every line of the file in a string
2. when the program reads the '\n' from the file stores the word which is stored in the string to the array

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

int main()
{
    FILE *fp;

    fp = fopen("C:\\Users\\Docs\\lol.txt", "r");

    if (fp == NULL)
    {
        printf("the file is empty");
        exit(8);
    }

    int length[4];
    int ch1;
    int counter1 = 0, i = 0;

    while ((ch1 = getc(fp)) != EOF)
    {
        if (ch1 == '\n')
        {
            length[i] = counter1;
            i++;
            counter1 = 0;
            continue;
        }
        counter1++;
    }
    length[i] = counter1;

    fseek(fp, 0, SEEK_SET);

    int thelongest = length[0];

    for (i = 0; i < counter; i++)
    {
        if (length[i] >= thelongest)
        {
            thelongest = length[i];
        }
    }

    printf("\n the longest number is %d", thelongest);

    char **arr;

    **arr = (char **)malloc(sizeof(char *) * 4);

    int j = 0 i = 0;
    char str[thelongest];
    int ch2;
    while ((ch2 = getc(fp)) != EOF)
    { // printf("fvfdvdfvd");
        if (ch2 == '\n')
        {
            arr[j] = (char *)malloc(thelongest * sizeof(char));
            strcpy(arr[j], str);
            // printf("\n%c",str[i]);
            j++;
            continue;
        }
        str[i] = ch2;
        i++;
    }
    str[i] = ch2;
    strcpy(arr[j], str);

    return 0;
}

Answer 1

There are multiple problems:

• the diagnostic message is incorrect if fopen fails

• you have undefined behavior if the file has more than 4 lines

• **arr = (char **)malloc(sizeof(char *) * 4); is incorrect! you should write:

   arr = malloc(sizeof(*aff) * count);
  

• char str[thelongest]; is not long enough to store a string of length thelongest: you need an extra byte for the null terminator.

• arr[j] = (char *)malloc(thelongest * sizeof(char)); is too short for the longest lines and too large for other ones. You should use strdup() or allocate i + 1 bytes.

• you must set a null byte at s[i] before you can use strcpy(arr[j], str);

• you mist reset i to 0 after storing the word in the array.

• str[i] = ch2; after the final loop is incorrect: ch2 has the value EOF, which is not a character. You should set str[i] = '\0' and copy the last line if i != 0.

Here is a modified version:

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

int main() {
    const char *filename = "C:\\Users\\Docs\\lol.txt";
    FILE *fp = fopen(, "r");
    if (fp == NULL) {
        fprintf(stderr, "cannot open file %s: %s\n", filename, strerror(errno));
        exit(8);
    }

    // compute the number of lines and the maximum length
    int len = 0, longest = 0, count = 0;
    for (;;) {
        int c = getc(fp);
        if (c == EOF || c == '\n') {
            if (longest < len)
                longest = len;
            if (len > 0)
                count++;
            len = 0;
            if (c == EOF)
                break;
        } else {
            len++;
        }
    }

    printf("the longest line has %d bytes\n", longest);
    printf("%d non empty lines\n", count);

    // allocate the array with an extra entry for a NULL terminator
    char **arr = calloc(sizeof(**arr), count + 1);
    if (arr == NULL) {
        fprintf(stderr, "cannot allocate memory\n");
        fclose(fp);
        return 1;
    }

    // read the file contents
    char str[thelongest + 1];
    int i = 0, j = 0;
    rewind(fp);
    for (;;) {
        int c = getc(fp);
        if (c == '\n' || c == EOF) {
            // store a new word
            if (j != 0) {
                str[j] = '\0';
                arr[i++] = strdup(str);
                j = 0;
            }
            if (c == EOF)
                break;
        } else {
            str[j++] = c;
        }
    }
    arr[i] = NULL;
    fclose(fp);

    // do something with the array
    [...]
    // free the array
    for (i = 0; i < count; i++)
        free(arr[i]);
    free(arr);
    return 0;
}