17.10 Case Study: Inline Functions Versus Normal Functions

I once worked on writing a word-processing program for a large computer manufacturer. We had a function next_char that was used to get the next character from the current file. It was used in thousands of places throughout the program. When we first tested the program with next_char written as a function, the program was unacceptably slow. Analyzing our program, we found that 90 percent of the time was spent in next_char. So we changed it to an inline function. The speed doubled; however, our code size went up 40 percent and required a memory expansion card to work. So the speed was all right, but the size was unacceptable. We finally had to write the routine as a function in hand-optimized assembly language to get both the size and the speed to acceptable levels.