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Uses of Typedef

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Programming Fundamentals

Université Duke

4.7 (1,522 évaluations) | 43K étudiants inscrits

Cours 1 de 4 dans Introduction to Programming in C Spécialisation

Programming is an increasingly important skill, whether you aspire to a career in software development, or in other fields. This course is the first in the specialization Introduction to Programming in C, but its lessons extend to any language you might want to learn. This is because programming is fundamentally about figuring out how to solve a class of problems and writing the algorithm, a clear set of steps to solve any problem in its class. This course will introduce you to a powerful problem-solving process—the Seven Steps—which you can use to solve any programming problem. In this course, you will learn how to develop an algorithm, then progress to reading code and understanding how programming concepts relate to algorithms.

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Compétences que vous apprendrez

Algorithms, Programming Language Concepts, Problem Solving, C Programming

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4.7 (1,522 évaluations)

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Apr 21, 2019

I love the focus of this first course in the specialization is about problem solving and developing a mindset for programming. The course is well thought out and concepts are clearly explained!

MM

Dec 27, 2017

Well worth it! Hated it in the beginning, couldn't wrap my head around the algorithms, but the course studies helped, kept reading, watching the videos, FINALLY got it!\n\n100% can recommend!

À partir de la leçon

Types

Everything is a number to a computer, but types determine the size and interpretation of numbers. In this module you will learn about types beyond integers, both their conceptual representations, and their hardware representations in binary. You will learn basic data types, "non-number" types, and complex, custom types, as well as some important caveats, so you will avoid type-related programming mistakes.

Struct for a Rectangle2:12

Uses of Typedef3:12

Enumerated Types3:24

Enseigné par

Andrew D. Hilton
Associate Professor of the Practice
Genevieve M. Lipp
Assistant Professor of the Practice
Anne Bracy
Senior Lecturer

Transcription

Here we have a struct declaration for a rectangle. When you declare a struct, the struct tag, in this case rect_tag, identifies the struct's type. But by itself is not a type name. When you want to name the struct type, you have to include the struct keyword, like you see here. Many programmers find it tedious to right struct everywhere they need to use fixed struct types so they use typedef to define a new type name for the struct type. One way to use typedef with our rectangle struct is shown here. The typedef keywords says that we are going to make a new name for an existing type. The new name in this case rect_t comes last in the declaration and the name of the existing type comes between them. Notice that here the existing type is struct rect_tag. Now we can just use rect_t as a type name. It is an alias or another name for struct rect_tag. There are a couple of other ways we can do the same thing with typedef. We mention them all so that if you see one or the other ways in someone else's code, you will not be confused. We can combine the struct declaration and typedef into one statement. This follows the same rules we just discussed. The new name rect_t goes at the end of the typedef statement. And the existing type goes between the new name and the typedef keyword. It just happens that here the existing type gets declared in the typedef statement. The third option is the same as the previous one, except that the struct tag is omitted. This makes a struct with no tag and immediately aliases this struct to rect_t. Typedef has uses beyond just structs. Sometimes, we are writing some code that deals with RGB values for pixels. In this hypothetical example, we initially use unsigned ints to represent the red, green, or blue components of each pixel. But what happens if later we realize that it would be better to use an unsigned char since RGB values can only be between 0 and 255 and we don't want to waste memory. With the way we wrote the code, we have to go find every single place that we used unsigned int to represent an RGB value and change it. We can't even use the search and replace functionality of our editor since there may be other uses of unsigned int that do not represent RGB values. So we don't want to change them. Such a change is tedious and error-prone. In fact, one important rule of programming is to write code so that if you have to change something, you only have to change it in one place. Now suppose we had originally written our code this way. Here we used typedef to make rgb_t an alias for unsigned int. And then used rgb_t as the type name everywhere we needed to talk about an RGB pip value. With this code, if we want to change the type we use for RGB values, we can just change the typedef statement and everything else will change correctly. As a side benefit, this helps the readability of our code. Anyone reading the code can tell when a variable, parameter, or return value is an RGB value since its type is rgb_t. Typedef can be great to make your code easier to modify and easier to read.

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