Why to store a function parameter value in a class private variable?

up vote
1
down vote

favorite

I'm just curious, I'm going through a C++ library for the mcu2.4 TFT display.

And this method I notice when I run through C++ libraries.

Which is when a parameter is passed through a function, it's stored in a private variable; like this one:

HCTFT::HCTFT(byte DisplayType)

{

    _Display = DisplayType;

What's the benefit of this method? What's the similar method when I want to do it in C code?

asked 1 hour ago

Perch Eagle

558

add a comment |

up vote
1
down vote

favorite

I'm just curious, I'm going through a C++ library for the mcu2.4 TFT display.

And this method I notice when I run through C++ libraries.

Which is when a parameter is passed through a function, it's stored in a private variable; like this one:

HCTFT::HCTFT(byte DisplayType)

{

    _Display = DisplayType;

What's the benefit of this method? What's the similar method when I want to do it in C code?

asked 1 hour ago

Perch Eagle

558

add a comment |

up vote
1
down vote

favorite

I'm just curious, I'm going through a C++ library for the mcu2.4 TFT display.

And this method I notice when I run through C++ libraries.

Which is when a parameter is passed through a function, it's stored in a private variable; like this one:

HCTFT::HCTFT(byte DisplayType)

{

    _Display = DisplayType;

What's the benefit of this method? What's the similar method when I want to do it in C code?

asked 1 hour ago

Perch Eagle

558

I'm just curious, I'm going through a C++ library for the mcu2.4 TFT display.

And this method I notice when I run through C++ libraries.

Which is when a parameter is passed through a function, it's stored in a private variable; like this one:

HCTFT::HCTFT(byte DisplayType)

{

    _Display = DisplayType;

What's the benefit of this method? What's the similar method when I want to do it in C code?

c++ c class

asked 1 hour ago

Perch Eagle

558

asked 1 hour ago

Perch Eagle

558

asked 1 hour ago

Perch Eagle

558

asked 1 hour ago

Perch Eagle

558

asked 1 hour ago

Perch Eagle

558

add a comment |

3 Answers
3

active

oldest

votes

up vote
2
down vote

accepted

The reason is that _Display will be used probably after its construction.

So you pass the byte during construction, and afterwards the value is available during the object's lifetime.

In C you probably will do this by:

Passing the variable (byte DisplayType) in each function where the value is needed (you can use this way in C++ too but it's cumbersome in both C/C++ to pass the variable in all functions needed).

Storing it in a global variable (static for that .c file); this is the typically C method.

answered 1 hour ago

Michel Keijzers

6,31341737

1

OK, I understand, so it's a programming style. Hmm alright, I'm starting to understand C++ syntax. I'm just running through the library. Most of the time when I run through C++ libraries I encounter things; like, private, public, inline, virtual .. etc. There are also things I want to understand too, I'm just taking it step at a time to get to know C++ better, I'm thinking how C++ would be effective to me when I want to write a library.
– Perch Eagle
1 hour ago

Well in C++ (or actually an OO language) it's very normal to put information (data/variables) and functionality together, and in a class (private) variable you store data that belongs to that instance of the class.
– Michel Keijzers
47 mins ago

OK, this one is clear to me now, so the class is just a complete object which has its own functions and variables and that's it. Then also there are other specifiers which provide the property to use this class functions or variable by other classes but of course it's much more advanced topic than my current knowledge.
– Perch Eagle
42 mins ago

add a comment |

up vote
2
down vote

Michel Keijzers explained pretty well the purpose of that idiom. Just to
complement his answer, you can do exactly the same in C, only with a
slightly different syntax:

typedef struct {

    byte _Display;

    // ...

} HCTFT;



HCTFT_construct(HCTFT *this, byte DisplayType)

{

    this->_Display = DisplayType;

    // ...

}

Now, every function that receives a pointer to an HCTFT (a HCTFT
“method”) has access to that data as a member of the struct.

answered 1 hour ago

Edgar Bonet

23.7k22344

So you mean I have to store it somewhere whether in a class private member with C++, struct variable with C or a global variable. So I don't have to pass it again to other functions, and I just can call its value from any function without passing it to that function? Am I understanding it correctly?
– Perch Eagle
1 hour ago

1

@PerchEagle: You don't have to: there are always many ways to do one thing. What I say is that, if you need to store several pieces of data for managing a TFT display, it is convenient to bundle them together into a single data structure (a struct). Then, instead of passing all the pieces as separate arguments to every function that deals with the display, you just pass a pointer to that single struct. The code becomes better structured and more readable. The C++ classes and methods are basically syntactic sugar over this programming pattern.
– Edgar Bonet
45 mins ago

Wonderful, I just have to dive into writing the TFT library to learn how to use these skills, I started to put the definitions in the header file. But what I'm considering now is that the process could be similar if I used my basic C skills to write a library hmmm. I found a good example like this piece of code. void HCTFT::SetFG(byte R, byte G, byte B) { _FGR = R; _FGG = G; _FGB = B; } so now the result is that the underscore variables are declared in the private section. And now by passing them to this function then they can be used right away in other functions! Nice.
– Perch Eagle
34 mins ago

add a comment |

up vote
1
down vote

That is more Object Oriented Programing question than the Arduino related.

Encapsulation is one of the fundamentals of OOP and it's basically you'll provide some interface to the object and the outside world doesn't have to know anything about it's internals (so it's not possible to change it into inconsistent state).

answered 1 hour ago

KIIV

3,5271617

add a comment |

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3 Answers
3

active

oldest

votes

3 Answers
3

active

oldest

votes

up vote
2
down vote

accepted

The reason is that _Display will be used probably after its construction.

So you pass the byte during construction, and afterwards the value is available during the object's lifetime.

In C you probably will do this by:

Passing the variable (byte DisplayType) in each function where the value is needed (you can use this way in C++ too but it's cumbersome in both C/C++ to pass the variable in all functions needed).

Storing it in a global variable (static for that .c file); this is the typically C method.

answered 1 hour ago

Michel Keijzers

6,31341737

1

OK, I understand, so it's a programming style. Hmm alright, I'm starting to understand C++ syntax. I'm just running through the library. Most of the time when I run through C++ libraries I encounter things; like, private, public, inline, virtual .. etc. There are also things I want to understand too, I'm just taking it step at a time to get to know C++ better, I'm thinking how C++ would be effective to me when I want to write a library.
– Perch Eagle
1 hour ago

Well in C++ (or actually an OO language) it's very normal to put information (data/variables) and functionality together, and in a class (private) variable you store data that belongs to that instance of the class.
– Michel Keijzers
47 mins ago

OK, this one is clear to me now, so the class is just a complete object which has its own functions and variables and that's it. Then also there are other specifiers which provide the property to use this class functions or variable by other classes but of course it's much more advanced topic than my current knowledge.
– Perch Eagle
42 mins ago

add a comment |

up vote
2
down vote

accepted

The reason is that _Display will be used probably after its construction.

So you pass the byte during construction, and afterwards the value is available during the object's lifetime.

In C you probably will do this by:

Passing the variable (byte DisplayType) in each function where the value is needed (you can use this way in C++ too but it's cumbersome in both C/C++ to pass the variable in all functions needed).

Storing it in a global variable (static for that .c file); this is the typically C method.

answered 1 hour ago

Michel Keijzers

6,31341737

1

OK, I understand, so it's a programming style. Hmm alright, I'm starting to understand C++ syntax. I'm just running through the library. Most of the time when I run through C++ libraries I encounter things; like, private, public, inline, virtual .. etc. There are also things I want to understand too, I'm just taking it step at a time to get to know C++ better, I'm thinking how C++ would be effective to me when I want to write a library.
– Perch Eagle
1 hour ago

Well in C++ (or actually an OO language) it's very normal to put information (data/variables) and functionality together, and in a class (private) variable you store data that belongs to that instance of the class.
– Michel Keijzers
47 mins ago

OK, this one is clear to me now, so the class is just a complete object which has its own functions and variables and that's it. Then also there are other specifiers which provide the property to use this class functions or variable by other classes but of course it's much more advanced topic than my current knowledge.
– Perch Eagle
42 mins ago

add a comment |

up vote
2
down vote

accepted

The reason is that _Display will be used probably after its construction.

So you pass the byte during construction, and afterwards the value is available during the object's lifetime.

In C you probably will do this by:

Passing the variable (byte DisplayType) in each function where the value is needed (you can use this way in C++ too but it's cumbersome in both C/C++ to pass the variable in all functions needed).

Storing it in a global variable (static for that .c file); this is the typically C method.

answered 1 hour ago

Michel Keijzers

6,31341737

The reason is that _Display will be used probably after its construction.

So you pass the byte during construction, and afterwards the value is available during the object's lifetime.

In C you probably will do this by:

Passing the variable (byte DisplayType) in each function where the value is needed (you can use this way in C++ too but it's cumbersome in both C/C++ to pass the variable in all functions needed).

Storing it in a global variable (static for that .c file); this is the typically C method.

answered 1 hour ago

Michel Keijzers

6,31341737

answered 1 hour ago

Michel Keijzers

6,31341737

answered 1 hour ago

Michel Keijzers

6,31341737

answered 1 hour ago

Michel Keijzers

6,31341737

1

OK, I understand, so it's a programming style. Hmm alright, I'm starting to understand C++ syntax. I'm just running through the library. Most of the time when I run through C++ libraries I encounter things; like, private, public, inline, virtual .. etc. There are also things I want to understand too, I'm just taking it step at a time to get to know C++ better, I'm thinking how C++ would be effective to me when I want to write a library.
– Perch Eagle
1 hour ago

Well in C++ (or actually an OO language) it's very normal to put information (data/variables) and functionality together, and in a class (private) variable you store data that belongs to that instance of the class.
– Michel Keijzers
47 mins ago

OK, this one is clear to me now, so the class is just a complete object which has its own functions and variables and that's it. Then also there are other specifiers which provide the property to use this class functions or variable by other classes but of course it's much more advanced topic than my current knowledge.
– Perch Eagle
42 mins ago

add a comment |

1

OK, I understand, so it's a programming style. Hmm alright, I'm starting to understand C++ syntax. I'm just running through the library. Most of the time when I run through C++ libraries I encounter things; like, private, public, inline, virtual .. etc. There are also things I want to understand too, I'm just taking it step at a time to get to know C++ better, I'm thinking how C++ would be effective to me when I want to write a library.
– Perch Eagle
1 hour ago

Well in C++ (or actually an OO language) it's very normal to put information (data/variables) and functionality together, and in a class (private) variable you store data that belongs to that instance of the class.
– Michel Keijzers
47 mins ago

OK, this one is clear to me now, so the class is just a complete object which has its own functions and variables and that's it. Then also there are other specifiers which provide the property to use this class functions or variable by other classes but of course it's much more advanced topic than my current knowledge.
– Perch Eagle
42 mins ago

OK, I understand, so it's a programming style. Hmm alright, I'm starting to understand C++ syntax. I'm just running through the library. Most of the time when I run through C++ libraries I encounter things; like, private, public, inline, virtual .. etc. There are also things I want to understand too, I'm just taking it step at a time to get to know C++ better, I'm thinking how C++ would be effective to me when I want to write a library.
– Perch Eagle
1 hour ago

Well in C++ (or actually an OO language) it's very normal to put information (data/variables) and functionality together, and in a class (private) variable you store data that belongs to that instance of the class.
– Michel Keijzers
47 mins ago

OK, this one is clear to me now, so the class is just a complete object which has its own functions and variables and that's it. Then also there are other specifiers which provide the property to use this class functions or variable by other classes but of course it's much more advanced topic than my current knowledge.
– Perch Eagle
42 mins ago

add a comment |

up vote
2
down vote

Michel Keijzers explained pretty well the purpose of that idiom. Just to
complement his answer, you can do exactly the same in C, only with a
slightly different syntax:

typedef struct {

    byte _Display;

    // ...

} HCTFT;



HCTFT_construct(HCTFT *this, byte DisplayType)

{

    this->_Display = DisplayType;

    // ...

}

Now, every function that receives a pointer to an HCTFT (a HCTFT
“method”) has access to that data as a member of the struct.

answered 1 hour ago

Edgar Bonet

23.7k22344

So you mean I have to store it somewhere whether in a class private member with C++, struct variable with C or a global variable. So I don't have to pass it again to other functions, and I just can call its value from any function without passing it to that function? Am I understanding it correctly?
– Perch Eagle
1 hour ago

1

@PerchEagle: You don't have to: there are always many ways to do one thing. What I say is that, if you need to store several pieces of data for managing a TFT display, it is convenient to bundle them together into a single data structure (a struct). Then, instead of passing all the pieces as separate arguments to every function that deals with the display, you just pass a pointer to that single struct. The code becomes better structured and more readable. The C++ classes and methods are basically syntactic sugar over this programming pattern.
– Edgar Bonet
45 mins ago

Wonderful, I just have to dive into writing the TFT library to learn how to use these skills, I started to put the definitions in the header file. But what I'm considering now is that the process could be similar if I used my basic C skills to write a library hmmm. I found a good example like this piece of code. void HCTFT::SetFG(byte R, byte G, byte B) { _FGR = R; _FGG = G; _FGB = B; } so now the result is that the underscore variables are declared in the private section. And now by passing them to this function then they can be used right away in other functions! Nice.
– Perch Eagle
34 mins ago

add a comment |

up vote
2
down vote

Michel Keijzers explained pretty well the purpose of that idiom. Just to
complement his answer, you can do exactly the same in C, only with a
slightly different syntax:

typedef struct {

    byte _Display;

    // ...

} HCTFT;



HCTFT_construct(HCTFT *this, byte DisplayType)

{

    this->_Display = DisplayType;

    // ...

}

Now, every function that receives a pointer to an HCTFT (a HCTFT
“method”) has access to that data as a member of the struct.

answered 1 hour ago

Edgar Bonet

23.7k22344

So you mean I have to store it somewhere whether in a class private member with C++, struct variable with C or a global variable. So I don't have to pass it again to other functions, and I just can call its value from any function without passing it to that function? Am I understanding it correctly?
– Perch Eagle
1 hour ago

1

@PerchEagle: You don't have to: there are always many ways to do one thing. What I say is that, if you need to store several pieces of data for managing a TFT display, it is convenient to bundle them together into a single data structure (a struct). Then, instead of passing all the pieces as separate arguments to every function that deals with the display, you just pass a pointer to that single struct. The code becomes better structured and more readable. The C++ classes and methods are basically syntactic sugar over this programming pattern.
– Edgar Bonet
45 mins ago

Wonderful, I just have to dive into writing the TFT library to learn how to use these skills, I started to put the definitions in the header file. But what I'm considering now is that the process could be similar if I used my basic C skills to write a library hmmm. I found a good example like this piece of code. void HCTFT::SetFG(byte R, byte G, byte B) { _FGR = R; _FGG = G; _FGB = B; } so now the result is that the underscore variables are declared in the private section. And now by passing them to this function then they can be used right away in other functions! Nice.
– Perch Eagle
34 mins ago

add a comment |

up vote
2
down vote

Michel Keijzers explained pretty well the purpose of that idiom. Just to
complement his answer, you can do exactly the same in C, only with a
slightly different syntax:

typedef struct {

    byte _Display;

    // ...

} HCTFT;



HCTFT_construct(HCTFT *this, byte DisplayType)

{

    this->_Display = DisplayType;

    // ...

}

Now, every function that receives a pointer to an HCTFT (a HCTFT
“method”) has access to that data as a member of the struct.

answered 1 hour ago

Edgar Bonet

23.7k22344

Michel Keijzers explained pretty well the purpose of that idiom. Just to
complement his answer, you can do exactly the same in C, only with a
slightly different syntax:

typedef struct {

    byte _Display;

    // ...

} HCTFT;



HCTFT_construct(HCTFT *this, byte DisplayType)

{

    this->_Display = DisplayType;

    // ...

}

Now, every function that receives a pointer to an HCTFT (a HCTFT
“method”) has access to that data as a member of the struct.

answered 1 hour ago

Edgar Bonet

23.7k22344

answered 1 hour ago

Edgar Bonet

23.7k22344

answered 1 hour ago

Edgar Bonet

23.7k22344

answered 1 hour ago

Edgar Bonet

23.7k22344

So you mean I have to store it somewhere whether in a class private member with C++, struct variable with C or a global variable. So I don't have to pass it again to other functions, and I just can call its value from any function without passing it to that function? Am I understanding it correctly?
– Perch Eagle
1 hour ago

1

@PerchEagle: You don't have to: there are always many ways to do one thing. What I say is that, if you need to store several pieces of data for managing a TFT display, it is convenient to bundle them together into a single data structure (a struct). Then, instead of passing all the pieces as separate arguments to every function that deals with the display, you just pass a pointer to that single struct. The code becomes better structured and more readable. The C++ classes and methods are basically syntactic sugar over this programming pattern.
– Edgar Bonet
45 mins ago

Wonderful, I just have to dive into writing the TFT library to learn how to use these skills, I started to put the definitions in the header file. But what I'm considering now is that the process could be similar if I used my basic C skills to write a library hmmm. I found a good example like this piece of code. void HCTFT::SetFG(byte R, byte G, byte B) { _FGR = R; _FGG = G; _FGB = B; } so now the result is that the underscore variables are declared in the private section. And now by passing them to this function then they can be used right away in other functions! Nice.
– Perch Eagle
34 mins ago

add a comment |

So you mean I have to store it somewhere whether in a class private member with C++, struct variable with C or a global variable. So I don't have to pass it again to other functions, and I just can call its value from any function without passing it to that function? Am I understanding it correctly?
– Perch Eagle
1 hour ago

1

@PerchEagle: You don't have to: there are always many ways to do one thing. What I say is that, if you need to store several pieces of data for managing a TFT display, it is convenient to bundle them together into a single data structure (a struct). Then, instead of passing all the pieces as separate arguments to every function that deals with the display, you just pass a pointer to that single struct. The code becomes better structured and more readable. The C++ classes and methods are basically syntactic sugar over this programming pattern.
– Edgar Bonet
45 mins ago

Wonderful, I just have to dive into writing the TFT library to learn how to use these skills, I started to put the definitions in the header file. But what I'm considering now is that the process could be similar if I used my basic C skills to write a library hmmm. I found a good example like this piece of code. void HCTFT::SetFG(byte R, byte G, byte B) { _FGR = R; _FGG = G; _FGB = B; } so now the result is that the underscore variables are declared in the private section. And now by passing them to this function then they can be used right away in other functions! Nice.
– Perch Eagle
34 mins ago

So you mean I have to store it somewhere whether in a class private member with C++, struct variable with C or a global variable. So I don't have to pass it again to other functions, and I just can call its value from any function without passing it to that function? Am I understanding it correctly?
– Perch Eagle
1 hour ago

@PerchEagle: You don't have to: there are always many ways to do one thing. What I say is that, if you need to store several pieces of data for managing a TFT display, it is convenient to bundle them together into a single data structure (a struct). Then, instead of passing all the pieces as separate arguments to every function that deals with the display, you just pass a pointer to that single struct. The code becomes better structured and more readable. The C++ classes and methods are basically syntactic sugar over this programming pattern.
– Edgar Bonet
45 mins ago

Wonderful, I just have to dive into writing the TFT library to learn how to use these skills, I started to put the definitions in the header file. But what I'm considering now is that the process could be similar if I used my basic C skills to write a library hmmm. I found a good example like this piece of code. void HCTFT::SetFG(byte R, byte G, byte B) { _FGR = R; _FGG = G; _FGB = B; } so now the result is that the underscore variables are declared in the private section. And now by passing them to this function then they can be used right away in other functions! Nice.
– Perch Eagle
34 mins ago

add a comment |

up vote
1
down vote

That is more Object Oriented Programing question than the Arduino related.

answered 1 hour ago

KIIV

3,5271617

add a comment |

up vote
1
down vote

That is more Object Oriented Programing question than the Arduino related.

answered 1 hour ago

KIIV

3,5271617

add a comment |

up vote
1
down vote

That is more Object Oriented Programing question than the Arduino related.

answered 1 hour ago

KIIV

3,5271617

That is more Object Oriented Programing question than the Arduino related.

answered 1 hour ago

KIIV

3,5271617

answered 1 hour ago

KIIV

3,5271617

answered 1 hour ago

KIIV

3,5271617

answered 1 hour ago

KIIV

3,5271617

add a comment |

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