{"id":13393,"date":"2022-12-30T13:59:48","date_gmt":"2022-12-30T08:29:48","guid":{"rendered":"https:\/\/fastbitlab.com\/?p=13393"},"modified":"2023-08-05T16:54:50","modified_gmt":"2023-08-05T11:24:50","slug":"microcontroller-embedded-c-programming-lecture-151-typedef-and-structure","status":"publish","type":"post","link":"https:\/\/fastbitlab.com\/blog\/microcontroller-embedded-c-programming-lecture-151-typedef-and-structure\/","title":{"rendered":"Microcontroller Embedded C Programming Lecture 151| Typedef and structure"},"content":{"rendered":"
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Typedef and structure<\/span><\/strong><\/h1>\n
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In this article, let’s understand using the typedef keyword with structure.<\/span><\/p>\n

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Typedef keyword in ‘C’ is used to give an alias name to primitive and user defined data types.<\/span><\/p>\n

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Example<\/b><\/span><\/p>\n

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Figure 1. Typedef with Structure Example<\/figcaption><\/figure>\n

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Consider the above structure definition. Here, you use the ‘<\/span>struct<\/span>‘ keyword and you identify this structure with the name, that is<\/span> CarModel<\/span> (tag name). And when you want to create variables of this structure definition, then you have to mention this struct CarModel.  struct CarModel is a data type. <\/span><\/span><\/p>\n

Now instead of doing the first method(Fig a), you can also do the second method(Fig b).<\/span><\/p>\n

Instead of writing <\/span>struct CarModel <\/b> (this long name ), you can just finish it off in one word <\/span>CarModel_t<\/b>. So, this is what we call a <\/span>typedef name or an alias name<\/b>. <\/span><\/span><\/p>\n

For that, you have to create the structure in this fashion.<\/span><\/p>\n

First, you have to use two standard reserved keywords, <\/span>typedef struct<\/b><\/span> (There is a space in between). <\/span><\/span><\/p>\n

typedef struct<\/span> and don’t mention any tag name here, this is optional.  But, give an alias name to this structure. Like <\/span>CarModel_t<\/span> after the flower bracket (as shown in fig(b)). <\/span><\/span><\/p>\n

And after that, by just using that typedef name you can create the variables.  So, by using a typedef you can give an alias name.<\/span><\/p>\n

This is also used with primitive data types like integer, char, unsigned int, like that.  <\/span><\/p>\n

So, we have already used that when we include the file stdint.h. stdint.h has various typedef definitions for different primitive data types. <\/span><\/p>\n

And <\/span> _t<\/b> is just used to distinguish between an enum and a typedef. For example, for an enum will use _e. <\/span><\/span><\/p>\n

So, if you don’t mention this, what happens? It confuses the programmer. They don’t understand, whether it is an enum definition or whether it is a typedef definition. So, to resolve that confusion we just use _t here. So, there is no strict requirement that you should use _t. So, this is just done for readability purposes.<\/span><\/p>\n

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Let’s convert the below structure type program into a typedef structure.<\/span><\/p>\n

#include<stdio.h>\r\n<\/span>\r\nstruct<\/span> DataSet<\/span>\r\n{\r\n    char<\/span>  data1;\r\n    int<\/span>   data2;\r\n    char<\/span>  data3;\r\n    short<\/span> data4;\r\n}__attribute__<\/span>((packed));\r\n\r\n struct<\/span> DataSet<\/span> data; \/\/ this consumes 12 bytes in memory(RAM)<\/span><\/pre>\n
Structure type<\/span><\/p>\n
First, you have to remove the tag name DataSet and give the <\/span>typedef<\/b> keyword. <\/span><\/span><\/p>\n
And after that mention the alias name or typedef name. I write DataSet and for identification purposes that is a typedef name I use <\/span>_t<\/b>. <\/span><\/span><\/p>\n
#include<stdio.h>\r\n<\/span>\r\ntypedef struct<\/span>\r\n{\r\n    char<\/span>  data1;\r\n    int<\/span>   data2;\r\n    char<\/span>  data3;\r\n    short<\/span> data4;\r\n}DataSet_t<\/span>;<\/span>\r\n\r\nDataSet_t<\/span> data; \/\/ this consumes 12 bytes in memory(RAM)<\/span><\/pre>\n
Convert to Typedef structure type<\/span><\/p>\n
After that you need not write like <\/span>struct<\/b> DataSet data;<\/b> You can remove this and you can just mention the DataSet (typedef name), as shown in above code snippet. That’s how you can use a typedef struct.<\/span><\/span><\/p>\n
So, if you open the microcontroller device header file you will see lots of typedef structures. <\/span><\/p>\n
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Some more points about the structure<\/b><\/span><\/p>\n