perror and strerror functions - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print an error message using perror.

C

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

int main() {
    FILE *fp = fopen("nonexistent.txt", "r");
    if (fp == NULL) {
        [1]("File open error");
    }
    return 0;
}

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

Aperror

Bprintf

Cstrerror

Dfprintf

Attempts:

3 left

💡 Hint

Common Mistakes

Using printf instead of perror to print error messages.

The perror function prints a descriptive error message to stderr based on the current errno value.

2fill in blank

medium

Complete the code to get the error message string from errno using strerror.

C

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

int main() {
    int errnum = 2;
    printf("Error message: %s\n", [1](errnum));
    return 0;
}

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Aperror

Bfprintf

Cstrerror_r

Dstrerror

Attempts:

3 left

💡 Hint

Common Mistakes

Using perror instead of strerror to get error string.

The strerror function returns a pointer to the error message string corresponding to the error number.

3fill in blank

hard

Fix the error in the code to correctly print the error message using perror.

C

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

int main() {
    FILE *fp = fopen("missing.txt", "r");
    if (fp == NULL) {
        perror([1]);
    }
    return 0;
}

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ANULL

B"File error"

Cstrerror(errno)

Derrno

Attempts:

3 left

💡 Hint

Common Mistakes

Passing errno or NULL instead of a string to perror.

The perror function expects a string prefix to print before the error message. Passing a string literal like "File error" is correct.

4fill in blank

hard

Fill both blanks to create a dictionary-like mapping of error numbers to messages using strerror.

C

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

int main() {
    int errors[] = {1, 2, 3};
    for (int i = 0; i < 3; i++) {
        printf("Error %d: %s\n", errors[i], [1](errors[i]));
    }
    return [2];
}

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Astrerror

Bperror

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using perror inside the loop or returning 1 instead of 0.

Use strerror to get the error message string for each error number. Return 0 to indicate successful program completion.

5fill in blank

hard

Fill all three blanks to print an error message using strerror and return an error code.

C

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

int main() {
    FILE *fp = fopen("file.txt", "r");
    if (fp == NULL) {
        fprintf(stderr, "Error opening file: %s\n", [1]([2]));
        return [3];
    }
    fclose(fp);
    return 0;
}

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Aperror

Berrno

C1

Dstrerror

Attempts:

3 left

💡 Hint

Common Mistakes

Using perror inside fprintf or returning 0 on error.

strerror(errno) returns the error message string for the last error. Returning 1 indicates an error exit code.