Sams Teach Yourself C in 21 Days

The program in Listing 15.7 is the most complex you have yet encountered in this book.

It uses many of the C programming techniques that were covered in previous lessons.

With the aid of the preceding explanation, you should be able to follow the program’s

operation and understand each step. If you find areas that are unclear to you, review the

related sections of this book until you understand.

Working with Pointers to Functions ..................................................................

Pointers to functions provide another way of calling functions. “Hold on,” you might be

thinking. “How can you have a pointer to a function? Doesn’t a pointer hold the address

where a variable is stored?”

Well, yes and no. It’s true that a pointer holds an address, but it doesn’t have to be the

address where a variable is stored. When your program runs, the code for each function

is loaded into memory starting at a specific address. A pointer to a function holds the

starting address of a function—its entry point.

Why use a pointer to a function? As I mentioned earlier, it provides a more flexible way

of calling a function. It lets the program choose from among several functions, selecting

the one that is appropriate for the current circumstances.

406 Day 15

FIGURE15.5

Before sorting, the

pointers are in the

same order in which

the strings were

entered.

FIGURE15.6

After sorting, the

pointers are ordered

according to the

alphabetical order of

the strings.

lines[0]

lines[1]

lines[2]

lines[3]

lines[4]

zoo\0

program\0zoo

applezo\0

dog\0

merrzy\0o

lines[0]

lines[1]

lines[2]

lines[3]

lines[4]

zoo\0

programzoo\0

applzoe\0

dog\0

merryzo\0

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