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1. Top results related to what are the function of dictionary keys in c programming

   • What are the benefits of function pointers in C?

     Top Answer

     Answered Jul 19, 2017 · 3 votes

     • Same as regular typdefs, incredibly useful for 2 and 4. Instead of typing the whole thing, you can now use myFuncDef
     • A function declaration for a function that recieves a function pointer. A function that takes a function pointer of 1. would thus look int add2to3(myFuncDef functionPtr);
     • -
     • A function that takes an int and (probably based on that) returns you a function pointer. Using the typedef it would have looked like myFuncDef functionFactory(int n);

     Without typedefs these chains of pointers to pointers could get incredibly long as can be seen in this question: C syntax for functions returning function pointers

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     1/5

   • What are the semantics of function pointers with empty parentheses in each C standard?

     Top Answer

     Answered Mar 25, 2018 · 2 votes

     N1570 6.11.6:

     The use of function declarators with empty parentheses (not prototype-format parameter type declarators) is an obsolescent feature.

     This same wording appears in the 1990, 1999, and 2011 editions of the ISO C standard. There has been no change. The word obsolescent says that the feature may be removed in a future edition of the Standard, but so far the committee has not done so. (Function pointer declarations are just one of several contexts where function declarators can appear.)

     The Introduction section of the C standard explains what obsolescent means:

     Certain features are obsolescent, which means that they may be considered for withdrawal in future revisions of this International Standard. They are retained because of their widespread use, but their use in new implementations (for implementation features) or new programs (for language [6.11] or library features [7.31]) is discouraged.

     A call to a function declared with an old-style declarator is still required to pass the correct number and type(s) of arguments (after promotion) as defined by the function's actual definition. A call with incorrect arguments has undefined behavior, which means that the compiler is not required to diagnose the error; the burden is entirely on the programmer.

     This is why prototypes were introduced, so that the compiler could check correctness of arguments.

     On an i386 system with GCC, “extra” arguments passed in a call to an empty-parentheses-type’d function pointer are ignored, because of how stack frames work ...

     Yes, that's well within the bounds of undefined behavior. The worst symptom of undefined behavior is having the program work exactly as you expect it to. It means that you have a bug that hasn't exhibited itself yet, and it will be difficult to track it down.

     You should not depend on that unless you have a very good reason to do so.

     If you change

     int (*fp)() = foo;-

     to

     int (*fp)(int) = foo;-

     the compiler will diagnose the incorrect call.

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     2/5

   • What are the different between calling constructor and calling function pointer of constructor in C++

     Top Answer

     Answered Jan 28, 2024 · 0 votes

     Calling a constructor and calling a function pointer of a constructor in C++ are very similar in the sense that they are both quite impossible:

     • You cannot call a constructor in C++.
     • You cannot obtain a pointer to a constructor in C++.

     According to the C++ spec about constructors:

     Constructors have no names and cannot be called directly.

     So, in C++, you do not call constructors. The language does that for you when you use the new keyword, when you declare an object on the stack, etc. The expression new MyClass() might look like a constructor invocation, and it does in fact contain a constructor invocation, and so it might be mistaken for a constructor invocation, but that's not what it is; it is a "new expression", which includes, among other things, an invocation of a constructor. But the other things are crucial: you cannot just skip them and directly invoke the constructor.

     Function pointers of constructors do not exist because normally you cannot take the address of a constructor. If you examine the names exported by the DLL, and somehow figure out which name corresponds to the constructor, and use that name to obtain the entry point of that constructor from the DLL, you are cheating: you are doing something which is not normally supported by the language. As a result, you should not attempt to invoke that entry point. A constructor is only supposed to be invoked by the language.

     Also according to the C++ spec:

     A constructor is a special non-static member function of a class.

     (Emphasis mine.)

     A constructor assumes that memory has been allocated, and proceeds to initialize that memory. The language takes care of the memory allocation, but invoking the constructor directly does not. Since a constructor is non-static, it expects an uninitialized this to be passed to it, but you are not allocating any memory and you are not passing anything to the constructor. The result is exactly as expected: a crash.

     And besides, think about it: the constructor could not be internally allocating the memory, because how would it work then if the object was allocated on the stack? And how would it work if the constructor was being invoked by the constructor of a derived class which presumably occupies more memory?

     You can get your DLL to work by using a factory method. A factory method is a public static method which executes new ClassA() and returns the result, or declares ClassA() and returns it by value. Then, obtain the address of the factory method from the DLL, and invoke it.

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     3/5

   • What are the things that are allowed as keys in a python dictionary?

     Top Answer

     Answered Jul 21, 2018 · 1 votes

     A key must be immutable.

     That is the only limitations.For example, You can use a tuple as the key if the items within tuple are immutable : (1,2)

     But you can not do this ([1,2])

     Read up more about immutable and mutable types to get a clear idea.

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     4/5

   • What are the differences between pointer variable's value & address of normal variable and what are the special purpose of pointers in C?

     Top Answer

     Answered Jun 26, 2017 · 5 votes

     Answering questions in reverse order:

     C does not have array variables....but this is really just working with pointers with an alternative syntax.

     This is incorrect, and you need to toss that bookmark in the trash. It's a common misconception that arrays and pointers are the same thing, but they are not. An array expression will be converted to a pointer expression under most circumstances, and array subscripting is accomplished through pointer arithmetic, but an array object is an actual array, not a pointer.

     If pointer also keeps the variable's address in it and at the same time we can get the variable's address using & sign, can't we do the same task pointer does by deriving the address of any variable? I mean if I don't declare it as pointer and use it as int ptr = &i; in 2nd code snippet and use it as normal variable, what would be the differences?

     That code doesn't illustrate why pointers exist, or why they are useful.

     C actually requires us to use pointers in the following cases:

     • To write to a function's parameters;
     • To track dynamically allocated memory;

     Pointers also make dynamic data structures like trees and lists easy to implement, but they aren't required for it (unless you're using dynamic memory allocation in those structures).

     Writing to a function's parameters

     C passes all function arguments by value; the formal parameter in the function definition is a separate object in memory from the actual parameter in the function call, so any change to the formal parameter is not reflected in the actual parameter. For example, assume the following swap function:

     void swap( int a, int b ) { int t = a; a = b; b = t; }-

     This function exchanges the values in a and b. However, when we call the function as

     int x = 4, y = 5;swap( x, y );-

     the values of x and y won't be updated, because they are different objects than a and b. If we want to update x and y, we have to pass pointers to them:

     swap( &x, &y );-

     and update the function definition as follows:

     void swap( int *a, int *b ) { int t = *a; *a = *b; *b = t; }-

     Instead of swapping the contents of a and b, we swap the contents of the objects that a and b point to. This crops up all the time - think about the scanf function, and how you have to use the & operator on scalar arguments.

     Tracking dynamically allocated memory

     The dynamic memory allocation functions malloc, calloc, and realloc all return pointers to dynamic memory buffers; there's no variable associated with that memory as such.

     char *buffer = malloc( sizeof *buffer * some_length );-

     A pointer is the only way to track that memory.

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2. www.scholarhat.com › tutorial › cKeywords in C: List of Keywords - scholarhat.com

   www.scholarhat.com › tutorial › c

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   May 27, 2024 · Keywords are reserved words that convey a special meaning and purpose within the context of the language. They are used in the syntax and cannot be used as a variable name. Example: int a. Here int is a keyword that conveys, a is a variable that can store the value of integer data type.

3. www.geeksforgeeks.org › functions-programmingFunctions in Programming - GeeksforGeeks

   www.geeksforgeeks.org › functions-programming

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   May 28, 2024 · Functions in Programming is a block of code that encapsulates a specific task or related group of tasks. Functions are defined by a name, may have parameters and may return a value. The main idea behind functions is to take a large program, break it into smaller, more manageable pieces (or functions), each of which accomplishes a specific task.

4. en.wikipedia.org › wiki › C_(programming_language)C (programming language) - Wikipedia

   en.wikipedia.org › wiki › C_(programming_language)

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   1 day ago · C is an imperative procedural language, supporting structured programming, lexical variable scope, and recursion, with a static type system. It was designed to be compiled to provide low-level access to memory and language constructs that map efficiently to machine instructions, all with minimal runtime support.

5. en.wikipedia.org › wiki › C_syntaxC syntax - Wikipedia

   en.wikipedia.org › wiki › C_syntax

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   3 days ago · It is designed to allow for programs that are extremely terse, have a close relationship with the resulting object code, and yet provide relatively high-level data abstraction. C was the first widely successful high-level language for portable operating-system development. C syntax makes use of the maximal munch principle. Data structures.

6. www.scholarhat.com › tutorial › cData Structures in C

   www.scholarhat.com › tutorial › c

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   May 24, 2024 · In this C tutorial, we'll delve deep into the data structures used in the C language. We'll understand various types of data structures with examples. At the end of the tutorial, you'll differentiate different data structures based on their characteristics. Let's get started.

7. www.scholarhat.com › tutorial › cExpressions in C Programming - Types of Expressions in C ...

   www.scholarhat.com › tutorial › c

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   May 27, 2024 · An expression in C language is a combination of symbols, numbers, and/or text that produces a particular result. These expressions are evaluated and can be used to assign values to variables, perform mathematical operations, or execute different actions such as comparison and Boolean logic.

8. www.simplilearn.com › c-programming-articleWhat is C Programming? - Simplilearn

   www.simplilearn.com › c-programming-article

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   May 30, 2024 · C is the combination of both low level (assembly) and high-level programming languages; also, it can be used to write an application and interact with low-level system memory and hardware. It can be written on practically any operating system and even works in most handheld devices.