File Handling in C

File handling is an important aspect of programming in C. It allows us to read from and write to files, enabling us to store and retrieve data from external sources. In this guide, we will explore the basics of file handling in C and how to perform various file operations.

Opening a File

Before we can perform any operations on a file, we need to open it. The fopen() function is used to open a file, and it requires two arguments: the name of the file and the mode in which we want to open it.

The file modes can be:

• r: read mode
• w: write mode
• a: append mode

For example, to open a file named “data.txt” in read mode, we can use the following code:

FILE *file = fopen("data.txt", "r");

Reading from a File

Once a file is opened in read mode, we can read its contents using various functions. The most commonly used function is fscanf(), which reads formatted data from a file. It requires three arguments: the file pointer, the format specifier, and the address of the variable where the data will be stored.

Here is an example of reading integers from a file:

int num1, num2;
fscanf(file, "%d %d", &num1, &num2);

We can also read characters from a file using the fgetc() function, which reads a single character at a time. Here is an example:

char ch;
while ((ch = fgetc(file)) != EOF) {
  // do something with the character
}

Writing to a File

To write data to a file, we need to open it in write mode or append mode. The fprintf() function is used to write formatted data to a file. It requires two arguments: the file pointer and the format specifier.

Here is an example of writing integers to a file:

int num1 = 10, num2 = 20;
fprintf(file, "%d %d", num1, num2);

We can also write characters to a file using the fputc() function, which writes a single character to the file. Here is an example:

char ch = 'A';
fputc(ch, file);

Closing a File

After we are done with a file, it is important to close it using the fclose() function. This ensures that any changes made to the file are saved and the resources associated with the file are freed.

Here is an example of closing a file:

fclose(file);

Error Handling

When working with files, it is important to handle errors that may occur during file operations. The ferror() function can be used to check if an error has occurred. If an error has occurred, we can use the perror() function to print an error message.

Here is an example of error handling:

if (ferror(file)) {
  perror("Error");
}

By properly handling errors, we can ensure that our file handling code is robust and reliable.

File handling is a crucial part of programming in C. It allows us to work with external files and perform various operations such as reading, writing, and appending data. By understanding the basics of file handling and using the appropriate functions, we can effectively manage files and create programs that interact with external data sources.