Sams Teach Yourself C in 21 Days

Working with the Screen, Printer, and Keyboard 341

14

All these functions require that you include stdio.h. The function perror()may also

require stdlib.h. The functions vprintf()andvfprintf()also require stdargs.h. On

UNIX systems,vprintf()andvfprintf()may also require varargs.h. Your compiler’s

Library Reference will state whether any additional or alternative header files are needed.

An Example ..................................................................................................

The short program in Listing 14.1 demonstrates the equivalence of streams.

LISTING14.1 stream.c. The equivalence of streams

1: /* Demonstrates the equivalence of stream input and output. */

2: #include <stdio.h>

3:

4: int main( void )

5: {

6: char buffer[256];

7:

8: /* Input a line, then immediately output it. */

9:

10: puts(gets(buffer));

11:

12: return 0;

13: }

On line 10, the gets()function is used to input a line of text from the keyboard (stdin).

Becausegets()returns a pointer to the string, it can be used as the argument to puts(),

which displays the string on-screen (stdout). When run, this program inputs a line of

text from the user and then immediately displays the string on-screen.

DOtake advantage of the standard

input/output streams that C provides.

DON’Trename or change the standard

streams unnecessarily.

DON’Ttry to use an input stream such as

stdinfor an output function such as

fprintf().

DO DON’T

For a beginner learning to program C, using gets()is fine. For a real-world program,

however, you should use fgets()(explained later in today’s lesson) as gets()poses

some risks to program security.

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