Advanced Programming in the UNIX® Environment

ptg10805159

150 StandardI/O Library Chapter 5

any other operation on the stream, we can change the buffering if we want to, with the

setbuforsetvbuffunctions from the previous section.

An open stream is closed by callingfclose.

#include <stdio.h>

int fclose(FILE *fp);

Returns: 0 if OK,EOFon error

Any buffered output data is flushed beforethe file is closed. Any input data that may

be buffered is discarded. If the standardI/O library had automatically allocated a

buffer for the stream, that buffer is released.

When a process terminates normally,either by calling theexitfunction directly or

by returning from themainfunction, all standardI/O streams with unwritten buffered

data areflushed and all open standardI/O streams areclosed.

5.6 Reading and Writing a Stream

Once we open a stream, we can choose from among three types of unformatted I/O:

1. Character-at-a-time I/O.We can read or write one character at a time, with the
   standardI/O functions handling all the buffering, if the stream is buffered.


2. Line-at-a-time I/O. If we want to read or write a line at a time, we usefgets
   andfputs.Each line is terminated with a newline character,and we have to
   specify the maximum line length that we can handle when we callfgets.We
   describe these two functions in Section 5.7.


3. Direct I/O. This type of I/O is supported by thefreadandfwritefunctions.
   For each I/O operation, we read or write some number of objects, whereeach
   object is of a specified size. These two functions areoften used for binary files
   where we read or write a structurewith each operation. We describe these two
   functions in Section 5.9.
   The termdirect I/O,fromthe ISO C standard, is known by many names: binary I/O,
   object-at-a-time I/O, record-oriented I/O, or structure-oriented I/O. Don’t confuse
   this featurewith theO_DIRECT openflag supported by FreeBSD and Linux—they
   areunrelated.
   (Wedescribe the formatted I/O functions, such asprintfandscanf, in Section 5.11.)

Input Functions

Three functions allow us to read one character at a time.

#include <stdio.h>

int getc(FILE *fp);

int fgetc(FILE *fp);

int getchar(void);

All three return: next character if OK,EOFon end of file or error