File Handling in C Language

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File Handling in C Language

Whether you're building a text editor, log parser, or any other application that interacts with data stored on disk, mastering file handling in the C programming language is essential. In this guide, we'll explore the fundamentals of file handling in C, touching upon topics like file opening, closing, reading from files, writing to files, and file pointers.

Opening Files

To interact with files in C, we use the fopen() function, which takes two arguments: the file name and a mode string that specifies how we'd like to open the file. The mode string can include characters like r for reading, w for writing, and a for appending. For instance, fopen("example.txt", "r") opens the file "example.txt" for reading, while fopen("output.txt", "w") creates a new file called "output.txt" and opens it for writing.

Closing Files

After we finish interacting with a file, we need to close it using the fclose() function. Closing the file properly ensures that any pending data is written to disk and helps free up operating system resources. It's a good practice to close files as soon as they're no longer needed.

Reading from Files

To read data from a file in C, you can use the fgetc() function to read one character at a time. However, for more efficient reading, it's often better to use functions like fgets() or fread().

The fgets() function reads a line from a file and appends a null character to the end of the string. Here's an example:

char line[100];
FILE *file = fopen("input.txt", "r");
fgets(line, 100, file);
printf("The line is: %s", line);
fclose(file);

The fread() function reads a binary block of data into an array. You specify the size of the block, the array to store the data, and the number of elements to read.

char buffer[100];
FILE *file = fopen("input.bin", "rb");
fread(buffer, sizeof(char), 100, file);
printf("The buffer is: %s", buffer);
fclose(file);

Writing to Files

To write to a file, you can use functions like fprintf() or fputs(). The fprintf() function writes formatted output to a file, while fputs() writes a string to a file.

Here's an example of using fprintf():

FILE *file = fopen("output.txt", "w");
fprintf(file, "This is a line of text\n");
fprintf(file, "This is another line\n");
fclose(file);

And here's an example using fputs():

FILE *file = fopen("output.txt", "w");
char *line = "This is a line of text\n";
fputs(line, file);
fclose(file);

File Pointers

File pointers keep track of the current position in a file, so you can read and write data at specific locations. The fseek() function allows you to reposition the file pointer, and the ftell() function returns the current position of the file pointer.

Here's an example of using fseek() to reposition a file pointer:

FILE *file = fopen("input.txt", "r");
// Position the file pointer at the second line
fseek(file, 1, SEEK_SET);
char line[100];
fgets(line, 100, file);
printf("The second line is: %s", line);
fclose(file);

And here's an example of using ftell() to get the current position of the file pointer:

FILE *file = fopen("input.txt", "r");
long current_position = ftell(file);
printf("The current position in the file is: %ld\n", current_position);
fclose(file);

By learning and mastering these basic file handling techniques, you'll be well-equipped to create C programs that interact with files to read, write, and manipulate data in various ways.

Description

Explore the fundamentals of file handling in the C programming language, including topics like file opening, closing, reading from files, writing to files, and file pointers. Learn how to use functions like fopen(), fclose(), fgetc(), fgets(), fwrite(), fprintf(), fputs(), fseek(), and ftell() to work with files efficiently.

File Handling in C Language

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Questions and Answers

What function is used in C to open a file?

Which character is used in the mode string to open a file for appending in C?

What is the purpose of the `fclose()` function in C?

Which function is recommended for reading a line from a file in C?

If we want to open a file for writing in C, which mode string character should be used?

What is the purpose of using `fread()` function in C?

What function is used to read a binary block of data into an array?

Which function writes a formatted output to a file?

What is the purpose of the `fseek()` function in C file handling?

Which function is used to open a file for reading in binary mode?

In C file handling, which function is used to store data into an array by specifying the size of the block and the number of elements to read?

What does the `ftell()` function do in C file handling?

Study Notes