C ftell() Function

The C ftell() function is a useful tool for file manipulation and management in the C programming language. It allows you to determine the current position or offset within a file, which can be helpful for various tasks such as reading, writing, or seeking specific locations within a file.

How does ftell() work?

The ftell() function returns the current file position indicator for the given file stream. It takes a FILE pointer as its argument and returns a long integer value representing the offset from the beginning of the file. This offset is measured in bytes.

Here is the syntax for using the ftell() function:

long ftell(FILE *stream);

Let’s break down the syntax:

• FILE *stream: This is a pointer to a FILE object that represents the file you want to get the current position from.
• long: The ftell() function returns a long integer value, which represents the offset from the beginning of the file.

Example usage of ftell()

Let’s consider an example to better understand how the ftell() function works:

#include <stdio.h>

int main() {
   FILE *file = fopen("example.txt", "r");
   if (file == NULL) {
      printf("Failed to open the file.");
      return 1;
   }
   
   fseek(file, 0, SEEK_END);
   long fileSize = ftell(file);
   
   printf("The size of the file is %ld bytes.", fileSize);
   
   fclose(file);
   return 0;
}

In this example, we first open a file called “example.txt” in read mode using the fopen() function. We then check if the file was successfully opened. If not, we display an error message and return from the program.

Next, we use the fseek() function to move the file position indicator to the end of the file. The fseek() function allows us to set the position indicator to a specific location within the file. In this case, we set it to the end of the file by passing the SEEK_END constant as the third argument.

After setting the position indicator, we call the ftell() function to get the current offset from the beginning of the file. The ftell() function returns a long integer value representing the offset, which we store in the fileSize variable.

Finally, we display the size of the file in bytes using the printf() function and close the file using the fclose() function.

The C ftell() function is a valuable tool for file manipulation in C. It allows you to determine the current position within a file, which can be useful for various file-related operations. By understanding how to use ftell() effectively, you can enhance your file handling capabilities in C programming.