Fluent C

Chapter 4. Returning Data from C Functions

Returning data from a function call is a task you are faced with when writing any kind of code that is longer than 10 lines and that you intend to be maintainable. Returning data is a simple task—you simply have to pass the data you want to share between two functions—and in C you only have the option to directly return a value or to return data via emulated “by-reference” parameters. There are not many choices and there is not much guidance to give—right? Wrong! Even the simple task of returning data from C functions is already tricky, and there are many routes you can take to structure your program and your function parameters.

Especially in C, where you have to manage the memory allocation and deallocation on your own, passing complex data between functions becomes tricky because there is no destructor or garbage collector to help you clean up the data. You have to ask yourself: should the data be put on the stack, or should it be allocated? Who should allocate—the caller or the callee?

This chapter provides best practices on how to share data between functions. These patterns help C programming beginners to understand techniques for returning data in C, and they help advanced C programmers to better understand why these different techniques are applied.

Figure 4-1 shows an overview of the patterns discussed in this chapter and their relationships, and Table 4-1 provides a summary of the patterns.

Figure 4-1. Overview of patterns ...