Sams Teach Yourself C in 21 Days

18: printf(“errno = %d.\n”, errno);

19: exit(1);

20: }

21: else

22: {

23: puts(“File opened for reading.”);

24: fclose(fp);

25: }

26: return 0;

27: }

Enter file name: perror.c

File opened for reading.

Enter file name: notafile.xxx

You goofed!: No such file or directory

errno = 2.

This program prints one of two messages based on whether a file can be opened

for reading. Line 15 tries to open a file. If the file opens, the elsepart of the if

loop executes, printing the following message:

File opened for reading.

If there is an error when the file is opened, such as the file not existing, lines 17–19 of

theifloop execute. Line 17 calls the perror()function with the string “You goofed!”.

The error number is then printed. The result of entering a file that does not exist is

You goofed!: No such file or directory.

errno = 2

548 Day 19

LISTING19.4 continued

OUTPUT

ANALYSIS

DOcheck for possible errors in your pro-

grams. Never assume that everything is

okay.

DON’Tinclude the errno.h header file if

you aren’t going to use the symbolic

error constants listed in Table 19.2.

DO DON’T

Searching and Sorting ........................................................................................

Among the most common tasks that programs perform are searching and sorting data.

The C standard library contains general-purpose functions that you can use for each task.

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