Error handling in files in C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to open a file for reading.

C

#include <stdio.h>

int main() {
    FILE *file = fopen("data.txt", [1]);
    if (file == NULL) {
        perror("Error opening file");
        return 1;
    }
    fclose(file);
    return 0;
}

Drag options to blanks, or click blank then click option'

A"r"

B"w"

C"a"

D"rw"

Attempts:

3 left

💡 Hint

Common Mistakes

Using "w" which opens the file for writing and truncates it.

Using "a" which opens the file for appending.

"r" opens the file for reading. If the file does not exist, fopen returns NULL.

2fill in blank

medium

Complete the code to check if the file pointer is NULL after fopen.

C

FILE *fp = fopen("log.txt", "r");
if ([1] == NULL) {
    perror("Failed to open file");
    return 1;
}

Drag options to blanks, or click blank then click option'

Afp->error

Bfp

C*fp

Dfopen

Attempts:

3 left

💡 Hint

Common Mistakes

Dereferencing the pointer before checking if it is NULL.

Checking a member like fp->error which does not exist.

We check if the pointer returned by fopen is NULL to detect errors.

3fill in blank

hard

Fix the error in the code to properly close the file only if it was opened.

C

FILE *f = fopen("input.txt", "r");
if (f == NULL) {
    perror("Cannot open file");
    return 1;
}
// read file contents
[1](f);
return 0;

Drag options to blanks, or click blank then click option'

Aclosefile

Bfileclose

Cfclose

Dclose

Attempts:

3 left

💡 Hint

Common Mistakes

Using close() which is for low-level file descriptors.

Using made-up functions like closefile or fileclose.

Use fclose() to close a file opened with fopen().

4fill in blank

hard

Fill both blanks to read a line safely and check for errors.

C

#include <stdio.h>

char buffer[100];
FILE *file = fopen("notes.txt", "r");
if (file == NULL) {
    perror("Open failed");
    return 1;
}
if (fgets(buffer, [1], [2]) == NULL) {
    if (feof(file)) {
        printf("End of file reached\n");
    } else {
        perror("Read error");
    }
}
fclose(file);

Drag options to blanks, or click blank then click option'

A100

Bfile

Cstdin

D50

Attempts:

3 left

💡 Hint

Common Mistakes

Using stdin instead of the file pointer.

Using a buffer size smaller than the actual buffer.

fgets reads up to the buffer size (100) from the file pointer.

5fill in blank

hard

Fill all three blanks to write to a file and handle errors properly.

C

#include <stdio.h>

int main() {
    FILE *fp = fopen("output.txt", [1]);
    if (fp == NULL) {
        perror("File open error");
        return 1;
    }
    if (fprintf(fp, [2], [3]) < 0) {
        perror("Write error");
        fclose(fp);
        return 1;
    }
    fclose(fp);
    return 0;
}

Drag options to blanks, or click blank then click option'

A"w"

B"Hello, World!\n"

C"%s"

D"r"

Attempts:

3 left

💡 Hint

Common Mistakes

Opening the file in "r" mode which is read-only.

Passing the string directly without a format specifier.

Open the file for writing with "w", use a format string "%s" and pass the string to write.