Sams Teach Yourself C in 21 Days

TABLE14.1 The five standard streams

Name Streams Device

stdin Standard input Keyboard

stdout Standard output Screen

stderr Standard error Screen

stdprn* Standard printer Printer (LPT1:)

stdaux* Standard auxiliary Serial port (COM1:)

*Supported only under Windows and DOS—Not part of ANSI standard.

You have actually been using two of these streams already. Whenever you have used the

printf()orputs()functions to display text on-screen, you have used the stdout

stream. Likewise, when you use gets()orscanf()to read keyboard input, you use the

stdinstream. The standard streams are opened automatically, but other streams, such as

those used to manipulate information stored on disk, must be opened explicitly. You’ll

learn how to do this on Day 16. The remainder of this chapter deals with the standard

streams.

Using C’s Stream Functions ..............................................................................

The C standard library has a variety of functions that deal with stream input and output.

Most of these functions come in two varieties: one that always uses one of the standard

streams, and one that requires the programmer to specify the stream. These functions are

listed in Table 14.2. This table doesn’t list all of C’s input/output functions, nor are all of

the functions in the table covered in today’s lesson.

TABLE14.2 The standard library’s stream input/output functions

Uses One of the Requires a

Standard Streams Stream Name Description

printf() fprintf() Formatted output

vprintf() vfprintf() Formatted output with a variable argument list

puts() fputs() String output

putchar() putc(),fputc() Character output

scanf() fscanf() Formatted input

vscanf() vfscanf() Formatted input with a variable argument list

gets() fgets() String input

getchar() getc(),fgetc() Character input

perror() String output to stderronly

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