Sams Teach Yourself C in 21 Days

Packaging Code in Functions 119

5

You can keep your user-defined functions in a separate source-code file, apart from

main(). This technique is useful with large programs and when you want to use the same

set of functions in more than one program. This technique is discussed on Day 21,

“Advanced Compiler Use.”

Working with Inline Functions ..........................................................................

There is a special type of function that can be created in C. These are inline functions.

Older versions of C will most likely not support inline functions; however, compilers that

support the C-99 standard should have support.

Inline functions are generally small functions. When the compiler executes, it will try to

execute an inline function in the fastest manner possible. This may be done by copying

the function’s code into the calling function. Because execution of this code would be

placed right into the calling function’s code it is called “inline.”

A function is made inline by using the inlinekeyword. The following declares an inline

function called toInches:

inline int toInches( int Feet )

{

return (Feet/12);

}

When the toInches()function is used, the compiler will do its best to optimize it to be

fast. Be aware that although the general assumption is that the code will simply be

moved into the calling function, this is not a guarantee. The only guarantee is that the

compiler will do its best to optimize the use of the code in this function. You will use

inline functions the same way as any other function.

Summary ............................................................................................................

Today’s lesson introduced you to functions, an important part of C programming.

Functions are independent sections of code that perform specific tasks. When your pro-

gram needs a task performed, it calls the function that performs that task. The use of

FIGURE5.6

Place your function

prototypes before your

function definitions.

Generally the proto-

types are near the top

of your listing.

Function call func1(a, b, c);

Function header void func1(int x, int y, int z)

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