Error Handling During File Operations in C
Last Updated :
16 Apr, 2025
File operations are a common task in C programming, but they can encounter various errors that need to be handled gracefully. Proper error handling ensures that your program can handle unexpected situations, such as missing files or insufficient permissions, without crashing. In this article, we will learn how to handle some common errors during file operations in C.
Here are some common errors that can occur during file operations:
| Error | Cause |
|---|
| File Not Found | Trying to open a file that doesn’t exist. |
|---|
| Permission Denied | Insufficient permissions to access the file. |
|---|
| Disk Full | No space left on the disk for writing data. |
|---|
| File Already Exists | Attempting to create a file that already exists in w mode. |
|---|
| Invalid File Pointer | Using a null or invalid file pointer for file operations. |
|---|
| End-of-File (EOF) | Attempting to read past the end of the file. |
|---|
| File Not Open | Attempting to perform operations on a file that wasn’t opened successfully. |
|---|
Failure to check for errors then the program may behave abnormally therefore an unchecked error may result in premature termination for the program or incorrect output.
Error Handling Techniques
Below are some standard error handling techniques:
1. File Not Found Error
A file not found error can occur when opening a file in read mode (r) or append mode (a). Use fopen() and check for NULL. If it is, the error message can be printed using perror() function.
C
//Driver Code Starts{
#include <stdio.h>
int main() {
//Driver Code Ends }
// Try to open file in
// read mode
FILE *file = fopen("file.txt", "r");
// Check if the file
// is opened/found
if (file == NULL) {
perror("Error");
return 1;
}
fclose(file);
//Driver Code Starts{
return 0;
}
//Driver Code Ends }
Output
Error: No such file or directory
In the above program, fopen() returns a NULL pointer because the file is not present in the current directory, then the perror() function prints the error message.
2. Handle Permission Denied Error
If the file exists but the program lacks the required permissions, fopen() will fail and return NULL pointer. We can change the perror() output to “permission denied” as shown in the below snippet.
C
FILE *file = fopen("/restricted/file.txt", "w");
if (file == NULL) {
perror("Permission denied");
}
3. Handle Disk Full Error
When writing to a file, ensure the disk has enough space. Errors during file operations can be detected using ferror(). In the below program, we assume that there is no space in memory to store any data.
C
//Driver Code Starts{
#include <stdio.h>
int main() {
//Driver Code Ends }
FILE *fptr = fopen("file.txt", "w");
if (fptr == NULL) {
perror("Error opening file");
return 1;
}
fprintf(fptr, "Writing to file");
// Check error after performing
// write operation
if (ferror(fptr)) {
perror("Error writing to file");
}
fclose(fptr);
//Driver Code Starts{
return 0;
}
//Driver Code Ends }
Output
Error writing to file: Permission Denied
4. Handle File Already Exists
When creating a new file with fopen() in w mode, the existing file will be overwritten. To avoid this, we open a new file in wx mode because if file is already present then fopen() return NULL and set the EEXIST value to the errno. In the below program, we assume that “test.text” file is already present in current directory.
C
//Driver Code Starts{
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
int main() {
//Driver Code Ends }
FILE *fptr;
// Try to open the file in
// write mode
fptr = fopen("test.text", "wx");
if (fptr == NULL) {
// Check if the error is
// due to file already existing
if (errno == EEXIST)
printf("File already exist");
}
//Driver Code Starts{
// If we reach here, the file
// was created successfully
fprintf(fptr, "This is a new file.");
fclose(fptr);
return 0;
}
//Driver Code Ends }
Output
File already exist
5. Handle Invalid File Pointer
Always verify that the file pointer is not NULL before performing operations like reading or writing.
C
FILE *file = NULL;
if (file == NULL) {
printf("Invalid file pointer. File operations cannot proceed.\n");
}
6. Handle End-of-File (EOF)
When we are reading data from a file and the file pointer reaches the end of the file, we can use the feof() function to handle the end of the file.
C
//Driver Code Starts{
#include <stdio.h>
int main() {
FILE *file = fopen("test.txt", "r");
//Driver Code Ends }
// Check for eof while reading
char ch;
while ((ch = fgetc(file)) != EOF)
putchar(ch);
// Use feof() to make sure
// EOF occurred or not
if (feof(file))
printf("End of file reached.");
else if (ferror(file))
printf("Error reading the file.");
//Driver Code Starts{
fclose(file);
return 0;
}
//Driver Code Ends }
Output
End of file reached.
7. Handle File Not Open
Whenever we attempt to open a file and the file cannot be opened due to some error, the fopen() function returns NULL. We can handle this easily using an if-else statement.
C
#include <stdio.h>
int main() {
FILE *file = fopen("example.txt", "r");
if (file == NULL) {
printf("File could not be opened.\n");
} else {
printf("File opened successfully.\n");
fclose(file);
}
return 0;
}
Output
File could not be opened.
File Closing Error
Sometimes, when we are closing a file using the fclose() function and it fails to close the file due to an error, it returns -1.
C
//Driver Code Starts{
#include <stdio.h>
int main() {
//Driver Code Ends }
FILE *fptr = fopen("test.txt", "w");
fprintf(fptr, "Writing to file");
// Check file close properly
if(fclose(fptr) == -1)
printf("File closing error");
else
printf("File closed")
//Driver Code Starts{
return 0;
}
//Driver Code Ends }
Output
File closing error
Similar Reads
Employee Record System in C using File Handling
Employee Record System is software built to handle the primary housekeeping functions of a company. ERS helps companies keep track of all the employees and their records. It is used to manage the company using a computerized system. This software built to handle the records of employees of any compa
5 min read
C File Handling Programs
C Program to list all files and sub-directories in a directory C Program to count number of lines in a file C Program to print contents of file C Program to copy contents of one file to another file C Program to merge contents of two files into a third file C program to delete a file
1 min read
Menu driven program for all operations on doubly linked list in C
A Linked List is a linear data structure that consists of two parts: one is the data part and the other is the address part. A Doubly Linked List in contains three parts: one is the data part and the other two are the address of the next and previous node in the list. In this article, all the common
5 min read
Using goto for Exception Handling in C
Exceptions are runtime anomalies or abnormal conditions that a program encounters during its execution. C doesn’t provide any specialized functionality for this purpose like other programming languages such as C++ or Java. However, In C, goto keyword is often used for the same purpose. The goto stat
4 min read
How to Read a File Line by Line in C?
In C, reading a file line by line is a process that involves opening the file, reading its contents line by line until the end of the file is reached, processing each line as needed, and then closing the file. In this article, we will learn how to read a file line by line in C. Reading a File Line b
2 min read
How to Open and Close a File in C++?
In C++, we can open a file to perform read and write operations and close it when we are done. This is done with the help of fstream objects that create a stream to the file for input and output. In this article, we will learn how to open and close a file in C++. Open and Close a File in C++ The fst
2 min read
C++ Program to Get the List of Files in a Directory
Getting the list of files in a directory is one of the most common operations performed by the Filesystem of an OS. The file explorer application in most operating systems performs the same operation in the background. In this article, you will learn how to get the list of files in a directory using
4 min read
How to Get Error Message When ifstream Open Fails in C++?
In C++, the std::ifstream class is used to open a file for input operations. It associates an input stream to the file. However, due to some reasons, it may be unable to open the requested file. In this article, we will learn how to show an error message when the ifstream class fails to open the fil
2 min read
How to Delete a File in C++?
C++ file handling allows us to manipulate external files from our C++ program. We can create, remove, and update files using file handling. In this article, we will learn how to remove a file in C++. Delete a File in C++ To remove a file in C++, we can use the remove() function defined inside the
2 min read
How to Fix Undefined Reference Error in C++?
In C++, the undefined reference error typically occurs during the linking phase of compilation. This error indicates that the compiler knows about a function or variable (it has been declared), but it cannot find the actual implementation (definition) during the linking process. The linker needs to
2 min read