{"id":12226,"date":"2022-11-08T08:10:53","date_gmt":"2022-11-08T08:10:53","guid":{"rendered":"http:\/\/fastbitlab.com\/?p=12226"},"modified":"2023-09-20T15:30:09","modified_gmt":"2023-09-20T10:00:09","slug":"microcontroller-embedded-c-programming-lecture-129-const-type-qualifier","status":"publish","type":"post","link":"https:\/\/fastbitlab.com\/blog\/microcontroller-embedded-c-programming-lecture-129-const-type-qualifier\/","title":{"rendered":"Microcontroller Embedded C Programming Lecture 129| ‘const’ type qualifier"},"content":{"rendered":"
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‘const’ type qualifier<\/span><\/strong><\/h1>\n
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Type qualifiers in \u2018C\u2019<\/b><\/span><\/span><\/p>\n

There are two important type qualifiers in ‘C’. <\/span><\/p>\n

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  1. const <\/strong><\/span><\/li>\n
  2. volatile<\/strong><\/span><\/li>\n<\/ol>\n

    Applying these qualifiers to  a variable declarations  is called qualifying<\/i><\/strong> <\/span>the declarations. <\/span><\/p>\n

    These are very important qualifiers you should understand to write proper and bug free code for your embedded device. <\/span><\/p>\n

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    Definition of ‘qualifier’:<\/strong><\/span><\/p>\n

    The English meaning of the word ‘qualifier<\/strong><\/span>‘ is a word or phrase, especially an adjective, used to attribute a quality to another word, especially a noun.  <\/span><\/p>\n

    In programming, also the same case. We use ‘const’ and ‘volatile’ qualifiers to attribute a feature to a variable. <\/span><\/p>\n

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    ‘const’<\/span> type qualifier:<\/b><\/span><\/p>\n

    ‘const’<\/span> is a type qualifier in ‘C’ used to enforce read-only features on variables. <\/span>When you define a variable as ‘const,’ it becomes a read-only variable, meaning its value cannot be modified after initialization.<\/span><\/p>\n

    Consider the following example:<\/span><\/p>\n

    \"\"<\/p>\n

    Now consider uint8_t data1 =10<\/span> variable definition. Here, ‘data1’ is a variable of type uint8 and that is initialized to 10. And in the program, you can modify the value of that variable, which is allowed. So, the ‘data1’ value can be modified throughout the program. No issues with that.<\/span><\/p>\n

    But when you use ‘const’ qualifier with a variable definition, then this variable changes, it becomes read-only. uint8_t const data2 =10;<\/span>  Here ‘data2’ is called a constant variable or read-only variable. <\/span><\/p>\n

    And in the program, if you try to change the value of the data2 variable, then this will trigger a compilation error. This is not allowed. So, you have to initialize that variable when you define it. After that, you are not allowed to change the value of that variable. Because now it is a read-only variable. <\/span><\/p>\n

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    Let’s analyze the below statement. <\/span><\/p>\n

    \"const
    Figure 1. Analyze the statement<\/span><\/figcaption><\/figure>\n

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    Here uint8_t is the data type, we also call it as type specifier of a variable. \u2018const\u2019 is a type qualifier of a variable. And data1 is a variable and in this case, it is a read-only variable.  And here the value of the data1 is 10 and it is fixed at 10. The value of the data1 can’t be modified.<\/span><\/p>\n

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    Let’s understand the syntax of how you should use this ‘const’ keyword in the variable definition. <\/span><\/p>\n

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    Figure 2. Syntax<\/span><\/figcaption><\/figure>\n

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    There are two possible ways. <\/span><\/p>\n