Detecting EOF of a txt File in C

Question

I wrote this code which reads every char of my text and puts it into my char array. My Problem is that the end of the file is not detected and so the fscanf() returns after the end of the text every time the last char until my array is filled. How can I prevent that? I am programming in C.

My Code:

int main() {
    char array[50][50];
    char buff;
    FILE *cola = fopen("C:/Users/danie/Desktop/cola.txt", "r");

    for (int i = 0; i < 50; i++) {
        for (int k = 0; k < 50; k++) {
            fscanf(cola, "%c", &buff);
            array[i][k] = buff;
        }
    }

    fclose(cola);

    for (int i = 0; i < 50; i++) {
        for (int k = 0; k < 50; k++) {
            printf("%c", array[i][k]);
        }
    }
    return 0;
}

Thank you for your help.

Answer 1

fscanf() returns the number of successful conversions. You should test the return value and also handle newline characters specifically:

#include <stdio.h>

int main(void) {
    char array[50][50];
    char buff;
    FILE *cola = fopen("C:/Users/danie/Desktop/cola.txt", "r");

    if (cola == NULL) {
        return 1;
    }
    for (int i = 0; i < 50; i++) {
        for (int k = 0; k < 50; k++) {
            if (fscanf(cola, "%c", &buff) != 1 || buff == '\n') {
                array[i][k] = '\0';
                break;
            }
            array[i][k] = buff;
        }
    }
    fclose(cola);

    for (int i = 0; i < 50; i++) {
        for (int k = 0; k < 50 && array[i][k] != '\0'; k++) {
            printf("%c", array[i][k]);
        }
        printf("\n");
    }
    return 0;
}

The code can be simplified if you use getc() instead of fscanf() to read bytes from the file:

#include <stdio.h>

int main(void) {
    char array[50][51];
    int c, i, k, n;
    FILE *cola = fopen("C:/Users/danie/Desktop/cola.txt", "r");

    if (cola == NULL) {
        return 1;
    }
    for (n = 0; n < 50; n++) {
        for (k = 0; k < 50; k++) {
            if ((c = getc(cola)) == EOF || c == '\n') {
                break;
            }
            array[n][k] = c;
        }
        array[n][k] = '\0';
        if (c == EOF && k == 0)
            break;
    }
    fclose(cola);

    for (i = 0; i < n; i++) {
        puts(array[i]);
    }
    return 0;
}

Answer 2

Replace:

for (int i = 0; i < 50; i++) {
    for (int k = 0; k < 50; k++) {
        fscanf(cola, "%c", &buff);
        array[i][k] = buff;
    }
}

with:

for (int i = 0; i < 50; i++) {
    for (int k = 0; k < 50; k++) {
        int c = getc(cola);
        if (c == EOF)
            break;
        array[i][k] = c;
    }
}

Since buff is then unused, don't define it. Note that the return type of getc() is an int, not just a char. Always check the I/O function for success/failure. In your original code, you don't even check whether the I/O operation succeeds, which makes detecting EOF impossible.

Note that this code makes a number of assumptions that may or may not be justifiable. For example, you assume each line in the file consists of 49 characters plus a newline; you also assume you'll never need to print the information as a 'string' (your existing code does not; it prints character by character, so it is 'safe').

You might want to describe the input as:

• Read up to 50 lines with up to 49 characters plus a newline in each line, storing the result in the variable array with each line being a null-terminated string.

This is more resilient to common problems (short lines, long lines, not enough lines). The code for that might be:

enum { LINE_LEN = 50, NUM_LINES = 50 };
char array[NUM_LINES][LINE_LEN];
int i;
for (i = 0; i < LINE_LEN; i++)
{
    int c;
    int k;
    for (k = 0; k < LINE_LEN; k++)
    {
        c = getc(cola);
        if (c == EOF || c == '\n')
            break;
        if (k == LINE_LEN - 1)
        {
            /* Too long - gobble excess */
            while ((c = getc(cola)) != EOF && c != '\n')
                ;
            break;
        }
        array[i][k] = c;
    }
    array[i][k] = '\0';
    if (c == EOF)
        break;
}
int num_lines = i;   // You have num_lines lines of data in your array

I found one version of the Coca Cola™ ASCII art image at https://www.ascii-code.com/ascii-art/logos/coca-cola.php which looks similar to what you have in your images, but there are many other sources and variants:

         __                              ___   __        .ama     ,
      ,d888a                          ,d88888888888ba.  ,88"I)   d
     a88']8i                         a88".8"8)   `"8888:88  " _a8'
   .d8P' PP                        .d8P'.8  d)      "8:88:baad8P'
  ,d8P' ,ama,   .aa,  .ama.g ,mmm  d8P' 8  .8'        88):888P'
 ,d88' d8[ "8..a8"88 ,8I"88[ I88' d88   ]IaI"        d8[         
 a88' dP "bm8mP8'(8'.8I  8[      d88'    `"         .88          
,88I ]8'  .d'.8     88' ,8' I[  ,88P ,ama    ,ama,  d8[  .ama.g
[88' I8, .d' ]8,  ,88B ,d8 aI   (88',88"8)  d8[ "8. 88 ,8I"88[
]88  `888P'  `8888" "88P"8m"    I88 88[ 8[ dP "bm8m88[.8I  8[
]88,          _,,aaaaaa,_       I88 8"  8 ]P'  .d' 88 88' ,8' I[
`888a,.  ,aadd88888888888bma.   )88,  ,]I I8, .d' )88a8B ,d8 aI
  "888888PP"'        `8""""""8   "888PP'  `888P'  `88P"88P"8m"

This file's longest line is the first at 67 characters plus newline; the shortest is 61 characters plus newline. The file only has 13 lines and 845 characters (LF line endings) in total. Thus, your program is ill-equipped to deal with this particular data file. It looks for 2,500 characters, and won't get them.

My complete test code was rigged to read from standard input, rather than a fixed file name.

#include <stdio.h>

int main(void)
{
    FILE *cola = stdin;

    enum { LINE_LEN = 80, NUM_LINES = 50 };
    char array[NUM_LINES][LINE_LEN];
    int i;      // Need value of i after loop
    for (i = 0; i < NUM_LINES; i++)
    {
        int c;  // Need value of c after loop
        int k;
        for (k = 0; k < LINE_LEN; k++)
        {
            c = getc(cola);
            if (c == EOF || c == '\n')
                break;
            if (k == LINE_LEN - 1)
            {
                /* Too long - gobble excess */
                while ((c = getc(cola)) != EOF && c != '\n')
                    ;
                break;
            }
            array[i][k] = c;
        }
        array[i][k] = '\0';
        if (c == EOF)
            break;
    }
    int num_lines = i;   // You have num_lines lines of data in your array

    for (i = 0; i < num_lines; i++)
        puts(array[i]);

    return 0;
}

I tested it on the data file shown, with an empty line at the end, and with a couple of lines containing more than 79 characters after the blank line. It handled all those special cases correctly. Note that handling user input is hard; handling perverse user input is harder. The code is less compact. You could change the rules and then change the code to match. I'm not sure this is the most minimal way to code this; it does work, however. It might be better to have a function to handle the inner input loop; the outer loop could test the return value from that function. This would cut down on the special case handling.

#include <assert.h>
#include <limits.h>
#include <stdio.h>

static int read_line(FILE *fp, size_t buflen, char *buffer)
{
    assert(buflen < INT_MAX);
    int c;      // Need value of c after loop
    size_t k;   // Need value of k after loop
    for (k = 0; k < buflen; k++)
    {
        if ((c = getc(fp)) == EOF || c == '\n')
            break;
        if (k == buflen - 1)
        {
            /* Too long - gobble excess */
            while ((c = getc(fp)) != EOF && c != '\n')
                ;
            break;
        }
        buffer[k] = c;
    }
    buffer[k] = '\0';
    return (k == 0 && c == EOF) ? EOF : (int)k;
}

int main(void)
{
    enum { LINE_LEN = 80, NUM_LINES = 50 };
    char array[NUM_LINES][LINE_LEN];
    int i;
    for (i = 0; i < NUM_LINES; i++)
    {
        if (read_line(stdin, LINE_LEN, array[i]) == EOF)
            break;
    }
    int num_lines = i;

    for (i = 0; i < num_lines; i++)
        puts(array[i]);

    return 0;
}

This produces the same output from the same input as the previous version.

Answer 3

int main() {
//char array[50][50];
char buff;
int t;
FILE *cola = fopen("C:/Users/danie/Desktop/cola.txt", "r");

if (cola == NULL)
{
    printf("Cannot open file \n");
    exit(0);
}
while (1) {
    t = fgetc(cola);
    if (t == EOF)
        break;
    buff = t;
    printf("%c", buff);
}


fclose(cola);

return 0;
}