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From Standard I/O to System I/O

Understand how C’s high-level standard I/O functions are built on top of low-level system calls, and learn the key differences in buffering, control, and error handling between <stdio.h> and system-level I/O.

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So far in this course, we have used C’s standard input and output functions such as printf(), scanf(), fopen(), fread(), and fprintf(). These functions are convenient, portable, and easy to use. However, they are not the lowest level at which input and output occur.

Underneath the functions declared in <stdio.h>, the operating system provides lower-level system calls that perform the actual data transfer. In this lesson, we examine how standard I/O relates to system I/O and understand the differences in buffering, error handling, and control.

Two layers of I/O in C

C programs typically interact with I/O at two different levels:

  1. Standard I/O (stdio library) is the high-level, portable interface provided by C. It includes functions like printf(), scanf(), fopen(), and fgets(). It is buffered, meaning data is temporarily stored in memory before being sent to the operating system, which improves performance and makes it easier to use. ...