I know the basics of this methods,procedures,function and classes but i always confuse to differentiate among those in contrast of Object oriented programming so please can any body tell me the difference among those with simple examples ?
A class, in current, conventional OOP, is a collection of data (member variables) bound together with the functions/procedures that work on that data (member functions or methods). The class has no relationship to the other three terms aside from the fact that it "contains" (more properly "is associated with") the latter.
The other three terms ... well, it depends.
A function is a collection of computing statements. So is a procedure. In some very anal retentive languages, though, a function returns a value and a procedure doesn't. In such languages procedures are generally used for their side effects (like I/O) while functions are used for calculations and tend to avoid side effects. (This is the usage I tend to favour. Yes, I am that anal retentive.)
Most languages are not that anal retentive, however, and as a result people will use the terms "function" and "procedure" interchangeably, preferring one to the other based on their background. (Modula-* programmers will tend to use "procedure" while C/C++/Java/whatever will tend to use "function", for example.)
A method is just jargon for a function (or procedure) bound to a class. Indeed not all OOP languages use the term "method". In a typical (but not universal!) implementation, methods have an implied first parameter (called things like this or self or the like) for accessing the containing class. This is not, as I said, universal. Some languages make that first parameter explicit (and thus allow to be named anything you'd like) while in still others there's no magic first parameter at all.
Edited to add this example:
The following untested and uncompiled C++-like code should show you what kind of things are involved.
class MyClass
{
int memberVariable;
void setMemberVariableProcedure(int v)
{
memberVariable = v;
}
int getMemberVariableFunction()
{
return memberVariable;
}
};
void plainOldProcedure(int stuff)
{
cout << stuff;
}
int plainOldFunction(int stuff)
{
return 2 * stuff;
}
In this code getMemberVariableProcedure and getMemberVariableFunction are both methods.
Procedures, function and methods are generally alike, they hold some processing statements.
The only differences I can think between these three and the places where they are used.
I mean 'method' are generally used to define functions inside a class, where several types of user access right like public, protected, private can be defined.
"Procedures", are also function but they generally represent a series of function which needs to be carried out, upon the completion of one function or parallely with another.
Classes are collection of related attributes and methods. Attributes define the the object of the class where as the methods are the action done by or done on the class.
Hope, this was helpful
Function, method and procedure are homogeneous and each of them is a subroutine that performs some calculations.
A subroutine is:
a method when used in Object-Oriented Programming (OOP). A method can return nothing (void) or something and/or it can change data outside of the subroutine or method.
a procedure when it does not return anything but it can change data outside of the subroutine, think of a SQL stored procedure. Not considering output parameters!
a function when it returns something (its calculated result) without changing data outside of the subroutine or function. This is the way how SQL functions work.
After all, they are all a piece of re-usable code that does something, e.g. return data, calculate or manipulate data.
There is no difference between of among.
Method : no return type like void
Function : which have return type
Related
I've been messing around with SDL2 in c and was wondering how to abstract code away without using too many function parameters. For example, in a normal gameplay loop there is usually an input, update, render cycle. Ideally, I would like this to be abstracted as possible so I could have functions called "input", "update", "render", in my loop. How could i do this in c without having those functions take a ludicrous amount of parameters? I know that c++ kind of solves this issue through classes, but I am curious and want to know how to do this in a procedural programming setting.
So far, I can't really think of any way to fix this. I tried looking it up online but only get results for c++ classes. As mentioned before, I want to stick to c because that is what i am comfortable with right now and would prefer to use.
If you have complex state to transport some between calls, put that in a struct. Pass a pointer to that as the sole argument to your functions, out at least as the first of very few.
That is a very common design pattern on C code.
void inputstep(struct state_t* systemstate);
void updatestep(struct state_t* systemstate);
void renderstep(struct state_t* systemstate, struct opengl_context_t* oglctx);
Note also that it is exactly the same, if not even more (due to less safety about pointers), overhead as having a C++ class with methods.
this in a functional programming setting.
Well, C is about as far as you get from a purely functional language, so functional programming paradigms only awkwardly translate. Are you sure you didn't mean "procedural"?
In a functional programming mindset, the state you pass into a function would be immutable or discarded after the function, and the function would return a new state; something like
struct mystate_t* mystate;
...
while(1) {
mystate = inputfunc(mystate);
mystate = updatefunc(mystate);
…
}
Only that in a functional setting, you wouldn't re-assign to a variable, and wouldn't have a while loop like that. Essentially, you wouldn't write C.
Say I have an external library that computes the optima, say minima, of a given function. Say its headers give me a function
double[] minimizer(ObjFun f)
where the headers define
typedef double (*ObjFun)(double x[])
and "minimizer" returns the minima of the function f of, say, a two dimensional vector x.
Now, I want to use this to minimize a parameterized function. I don't know how to express this in code exactly, but say if I am minimizing quadratic forms (just a silly example, I know these have closed form minima)
double quadraticForm(double x[]) {
return x[0]*x[0]*q11 + 2*x[0]*x[1]*q12 + x[1]*x[1]*q22
}
which is parameterized by the constants (q11, q12, q22). I want to write code where the user can input (q11, q12, q22) at runtime, I can generate a function to give to the library as a callback, and return the optima.
What is the recommended way to do this in C?
I am rusty with C, so asking about both feasibility and best practices. Really I am trying to solve this using C/Cython code. I was using python bindings to the library so far and using "inner functions" it was really obvious how to do this in python:
def getFunction(q11, q12, q22):
def f(x):
return x[0]*x[0]*q11 + 2*x[0]*x[1]*q12 + x[1]*x[1]*q22
return f
// now submit getFunction(/*user params*/) to the library
I am trying to figure out the C construct so that I can be better informed in creating a Cython equivalent.
The header defines the prototype of a function which can be used as a callback. I am assuming that you can't/won't change that header.
If your function has more parameters, they cannot be filled by the call.
Your function therefor cannot be called as callback, to avoid undefined behaviour or bogus values in parameters.
The function therefor cannot be given as callback; not with additional parameters.
Above means you need to drop the idea of "parameterizing" your function.
Your actual goal is to somehow allow the constants/coefficients to be changed during runtime.
Find a different way of doing that. Think of "dynamic configuration" instead of "parameterizing".
I.e. the function does not always expect those values at each call. It just has access to them.
(This suggests the configuration values are less often changed than the function is called, but does not require it.)
How:
I only can think of one simple way and it is pretty ugly and vulnerable (e.g. due to racing conditions, concurrent access, reentrance; you name it, it will hurt you ...):
Introduce a set of global variables, or better one struct-variable, for readability. (See recommendation below for "file-global" instead of "global".)
Set them at runtime to the desired values, using a separate function.
Initialise them to meaningful defaults, in case they never get written.
Read them at the start of the minimizing callback function.
Recommendation: Have everything (the minimizing function, the configuration variable and the function which sets the configuration at runtime) in one code file and make the configuration variable(s) static (i.e. restricts access to it this code file).
Note:
The answer is only the analysis that and why you should not try paraemeters.
The proposed method is not considered part of the answer; it is more simple than good.
I invite more holistic answers, which propose safer implementation.
This may come across as a strange question, since the convention is usually to have separate set and get methods. But in my case, it is a bit different: an argument to a function decides whether that function is a getter or a setter, so I am looking for a function name that will indicate such function.
Some names I have found were getset, setget, rw, and etc but i find these names rather strange. What kind of naming convention would fit for such functions?
Until Java beans came along with the get/set naming convention, one quite often saw functions (particularly methods in C++ and other OO languages) that did exactly as you describe.
They were often named after the variable that they set or got, e.g.:
int counter_;
int counter () {
return counter_;
}
int counter (int c) {
counter_ = c;
return counter_;
}
In languages with different namespaces for variables and functions, you could even have the variable and the get/set functions have exactly the same name (without the need for a trailing _ as I've shown here).
In languages with default parameters, you could potentially write the getter and setter as one function, e.g. something like this:
int counter (int c = MAX_INT) {
if (c != MAX_INT) {
counter_ = c;
}
return counter_;
}
... though I wasn't particularly keen on that approach because it led to subtle bugs if someone called counter (MAX_INT), for instance.
I always thought that this naming approach made some sense and I've written some libraries that worked that way.
This naming convention did, however, potentially confuse the reader of the code, particularly in languages where one could call a parameterless function without the trailing parentheses, so it was hard to see if a function was being called or if a public variable was being accessed directly. Of course some would call the latter a feature rather than a problem ...
How about just name the function after the name of the variable it populates? Like a property, when the parameter passed is null or other special value, then it is get, otherwise it is set.
What distinguishes and object from a struct?
When and why do we use an object as opposed to a struct?
How does an array differ from both, and when and why would we use an array as opposed to an object or a struct?
I would like to get an idea of what each is intended for.
Obviously you can blur the distinctions according to your programming style, but generally a struct is a structured piece of data. An object is a sovereign entity that can perform some sort of task. In most systems, objects have some state and as a result have some structured data behind them. However, one of the primary functions of a well-designed class is data hiding — exactly how a class achieves whatever it does is opaque and irrelevant.
Since classes can be used to represent classic data structures such as arrays, hash maps, trees, etc, you often see them as the individual things within a block of structured data.
An array is a block of unstructured data. In many programming languages, every separate thing in an array must be of the same basic type (such as every one being an integer number, every one being a string, or similar) but that isn't true in many other languages.
As guidelines:
use an array as a place to put a large group of things with no other inherent structure or hierarchy, such as "all receipts from January" or "everything I bought in Denmark"
use structured data to compound several discrete bits of data into a single block, such as you might want to combine an x position and a y position to describe a point
use an object where there's a particular actor or thing that thinks or acts for itself
The implicit purpose of an object is therefore directly to associate tasks with the data on which they can operate and to bundle that all together so that no other part of the system can interfere. Obeying proper object-oriented design principles may require discipline at first but will ultimately massively improve your code structure and hence your ability to tackle larger projects and to work with others.
Generally speaking, objects bring the full object oriented functionality (methods, data, virtual functions, inheritance, etc, etc) whereas structs are just organized memory. Structs may or may not have support for methods / functions, but they generally won't support inheritance and other full OOP features.
Note that I said generally speaking ... individual languages are free to overload terminology however they want to.
Arrays have nothing to do with OO. Indeed, pretty much every language around support arrays. Arrays are just blocks of memory, generally containing a series of similar items, usually indexable somehow.
What distinguishes and object from a struct?
There is no notion of "struct" in OOP. The definition of structures depends on the language used. For example in C++ classes and structs are the same, but class members are private by defaults while struct members are public to maintain compatibility with C structs. In C# on the other hand, struct is used to create value types while class is for reference types. C has structs and is not object oriented.
When and why do we use an object as opposed to a struct?
Again this depends on the language used. Normally structures are used to represent PODs (Plain Old Data), meaning that they don't specify behavior that acts on the data and are mainly used to represent records and not objects. This is just a convention and is not enforced in C++.
How does an array differ from both,
and when and why would we use an
array as opposed to an object or a
struct?
An array is very different. An array is normally a homogeneous collection of elements indexed by an integer. A struct is a heterogeneous collection where elements are accessed by name. You'd use an array to represent a collection of objects of the same type (an array of colors for example) while you'd use a struct to represent a record containing data for a certain object (a single color which has red, green, and blue elements)
Short answer: Structs are value types. Classes(Objects) are reference types.
By their nature, an object has methods, a struct doesn't.
(nothing stops you from having an object without methods, jus as nothing stops you from, say, storing an integer in a float-typed variable)
When and why do we use an object as opposed to a struct?
This is a key question. I am using structs and procedural code modules to provide most of the benefits of OOP. Structs provide most of the data storage capability of objects (other than read only properties). Procedural modules provide code completion similar to that provided by objects. I can enter module.function in the IDE instead of object.method. The resulting code looks the same. Most of my functions now return stucts rather than single values. The effect on my code has been dramatic, with code readability going up and the number of lines being greatly reduced. I do not know why procedural programming that makes extensive use of structs is not more common. Why not just use OOP? Some of the languages that I use are only procedural (PureBasic) and the use of structs allows some of the benefits of OOP to be experienced. Others languages allow a choice of procedural or OOP (VBA and Python). I currently find it easier to use procedural programming and in my discipline (ecology) I find it very hard to define objects. When I can't figure out how to group data and functions together into objects in a philosophically coherent collection then I don't have a basis for creating classes/objects. With structs and functions, there is no need for defining a hierarchy of classes. I am free to shuffle functions between modules which helps me to improve the organisation of my code as I go. Perhaps this is a precursor to going OO.
Code written with structs has higher performance than OOP based code. OOP code has encapsulation, inheritance and polymorphism, however I think that struct/function based procedural code often shares these characteristics. A function returns a value only to its caller and only within scope, thereby achieving encapsulation. Likewise a function can be polymorphic. For example, I can write a function that calculates the time difference between two places with two internal algorithms, one that considers the international date line and one that does not. Inheritance usually refers to methods inheriting from a base class. There is inheritance of sorts with functions that call other functions and use structs for data transfer. A simple example is passing up an error message through a stack of nested functions. As the error message is passed up, it can be added to by the calling functions. The result is a stack trace with a very descriptive error message. In this case a message inherited through several levels. I don't know how to describe this bottom up inheritance, (event driven programming?) but it is a feature of using functions that return structs that is absent from procedural programming using simple return values. At this point in time I have not encountered any situations where OOP would be more productive than functions and structs. The surprising thing for me is that very little of the code available on the internet is written this way. It makes me wonder if there is any reason for this?
Arrays are ordered collection of items that (usually) are of the same types. Items can be accessed by index. Classic arrays allow integer indices only, however modern languages often provide so called associative arrays (dictionaries, hashes etc.) that allow use e.g. strings as indices.
Structure is a collection of named values (fields) which may be of 'different types' (e.g. field a stores integer values, field b - string values etc.). They (a) group together logically connected values and (b) simplify code change by hiding details (e.g. changing structure layout don't affect signature of function working with this structure). The latter is called 'encapsulation'.
Theroretically, object is an instance of structure that demonstrates some behavior in response to messages being sent (i.e., in most languages, having some methods). Thus, the very usefullness of object is in this behavior, not its fields.
Different objects can demonstrate different behavior in response to the same messages (the same methods being called), which is called 'polymorphism'.
In many (but not all) languages objects belong to some classes and classes can form hierarchies (which is called 'inheritance').
Since object methods can work with its fields directly, fields can be hidden from access by any code except for this methods (e.g. by marking them as private). Thus encapsulation level for objects can be higher than for structs.
Note that different languages add different semantics to this terms.
E.g.:
in CLR languages (C#, VB.NET etc) structs are allocated on stack/in registers and objects are created in heap.
in C++ structs have all fields public by default, and objects (instances of classes) have all fields private.
in some dynamic languages objects are just associative arrays which store values and methods.
I also think it's worth mentioning that the concept of a struct is very similar to an "object" in Javascript, which is defined very differently than objects in other languages. They are both referenced like "foo.bar" and the data is structured similarly.
As I see it an object at the basic level is a number of variables and a number of methods that manipulate those variables, while a struct on the other hand is only a number of variables.
I use an object when you want to include methods, I use a struct when I just want a collection of variables to pass around.
An array and a struct is kind of similar in principle, they're both a number of variables. Howoever it's more readable to write myStruct.myVar than myArray[4]. You could use an enum to specify the array indexes to get myArray[indexOfMyVar] and basically get the same functionality as a struct.
Of course you can use constants or something else instead of variables, I'm just trying to show the basic principles.
This answer may need the attention of a more experienced programmer but one of the differences between structs and objects is that structs have no capability for reflection whereas objects may. Reflection is the ability of an object to report the properties and methods that it has. This is how 'object explorer' can find and list new methods and properties created in user defined classes. In other words, reflection can be used to work out the interface of an object. With a structure, there is no way that I know of to iterate through the elements of the structure to find out what they are called, what type they are and what their values are.
If one is using structs as a replacement for objects, then one can use functions to provide the equivalent of methods. At least in my code, structs are often used for returning data from user defined functions in modules which contain the business logic. Structs and functions are as easy to use as objects but functions lack support for XML comments. This means that I constantly have to look at the comment block at the top of the function to see just what the function does. Often I have to read the function source code to see how edge cases are handled. When functions call other functions, I often have to chase something several levels deep and it becomes hard to figure things out. This leads to another benefit of OOP vs structs and functions. OOP has XML comments which show up as tool tips in the IDE (in most but not all OOP languages) and in OOP there are also defined interfaces and often an object diagram (if you choose to make them). It is becoming clear to me that the defining advantage of OOP is the capability of documenting the what code does what and how it relates to other code - the interface.
I have one costly function that gets called many times and there is a very limited set of possible values for the parameter.
Function return code depends only on arguments so the obvious way to speed things up is to keep a static cache within the function for possible arguments and corresponding return codes, so for every combination of the parameters, the costly operation will be performed only once.
I always use this approach in such situations and it works fine but it just occurred to me that GCC function attributes const or pure probably can help me with this.
Does anybody have experience with this? How GCC uses pure and const attributes - only at compile time or at runtime as well?
Can I rely on GCC to be smart enough to call a function, declared as
int foo(int) __attribute__ ((pure))
just once for the same parameter value, or there is no guarantee whatsoever and I better stick to caching approach?
EDIT: My question is not about caching/memoization/lookup tables, but GCC function atributes.
I think you are confusing the GCC pure attribute with memoization.
The GCC pure attribute allows the compiler to reduce the number of times the function is called in certain circumstances (such as loop unrolling). However it makes no guarantees that it will do so, only if it think it's appropriate.
What you appear to be looking for is memoization of your function. Memoization is an optimization where calculations for the same input should not be repeated. Instead the previous result should be returned. The GCC pure attribute does not make a function work in this way. You would have to hand implement this.
I have one costly function that gets called many times and there is very limited set of possible values for the parameter.
Why not use a static constant map then (the arguments' can be hashed to generate a key, the return code the value)?
This sounds like it might be solved with a template function. If all if the known parameters and return values are known at compile-time, you could perhaps generate a template instance of the function for each possible parameter. Essentially you'd be calling a different instance of the function for each possible parameter. Not sure it would be any easier than the static cache you've already implemented, but might be worth exploring.
Check out template metaprogramming. The concepts are similar to 'memoization', suggested by JaredPar, even using the same introductory example of a factorial function. It might be appropriate to say that these kinds of templates are compile-time implementations of memoization.
I dont like to reopen old threads, but there was a particularly offensive comment here:
"templates are for dealing with different types, rather than different values of the same type"
Now, take a simple template factorial implementation:
template<int n> struct Factorial {
static const int value = n * Factorial<n-1>::value;
};
template<> struct Factorial<0> {
static const int value = 1;
};
The template parameter here is an integer, not a typename.