Difference between File Descriptor and File Pointer

File descriptor is simply an index into the file descriptor table. For each process in our operating system, there is a process control block(PCB). PCB keeps track of the context of the process. So one of the fields within this is an array called file descriptor table.

This array keeps track of all the resources that the process owns and can operate on. The file descriptor table holds pointers to the resources. Resources could be

• File
• Terminal I/O
• Pipes
• Socket for the communication channel between machines
• Any devices

So if any process opens or uses any resources will have an entry in the file descriptor table. Any process when it first starts is given access to three resources. These resources are:

• stdin
• stdout
• stderr

Understand this with an example. Suppose we are working on the terminal then input for it is stdin, the output is stdout and the error is stderr. And if we open any other terminal then both are two different processes now. The newly opened terminal will have its own stdin, stdout because it's a different process.

The file descriptor is just an integer that you get from the open() system call.

Example of file descriptor:

int fd = open(filePath, mode);

File pointer is a pointer returned by fopen() library function. It is used to identify a file. It is passed to a fread() and fwrite() function.

Example of file pointer:

FILE *fp;

fp = fopen("sample.txt,"a");

fprintf( fp, "Welcome to GFG");

fclose(fp);

File pointer provides high efficiency and high portability. It is buffered, unlike the file descriptor. Generally, we use a file pointer when we are reading from a file.

Following is a table of differences between File Descriptor and File Pointer