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

   • 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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   • 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. intellipaat.com › blog › tutorialFunctions in C - A Beginner's Guide - Intellipaat

   intellipaat.com › blog › tutorial

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   2 days ago · In C, a function is a self-contained block of code that performs a specific task. Functions offer several advantages, including code reusability, modularity, and better organization of code. A function can take input (parameters) and can produce output (return value) if necessary.

3. www.geeksforgeeks.org › extract-dictionary-valueExtract Dictionary Value from Column in Data Frame

   www.geeksforgeeks.org › extract-dictionary-value

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   3 days ago · The function to be passed to apply() will be a lambda function, which will extract each iterable from a particular column. Example: In this example, we create a data frame with two columns, one of them is of dictionary type. To extract the dictionary values, we then used apply() and lambda function to each keys of the dictionary.

4. People also ask

   What is a function in C?

   • In this article, we’ll delve deep into C functions, exploring their syntax, types, advantages, and best practices. In C, a function is a self-contained block of code that performs a specific task. Functions offer several advantages, including code reusability, modularity, and better organization of code.

   Functions in C - A Beginner's Guide - Intellipaat

   intellipaat.com/blog/tutorial/c-tutorial/c-functions/

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   Why is C a good programming language?

   • Programming languages are the building blocks of software development, and among them, the C programming language holds a special place. C is known for its simplicity, efficiency, and powerful features. One of the key elements that make C so versatile is its ability to define and use functions.

   Functions in C - A Beginner's Guide - Intellipaat

   intellipaat.com/blog/tutorial/c-tutorial/c-functions/

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   Which language is used for calling library functions in C?

   • Many languages support calling library functions in C, for example, the Python -based framework NumPy uses C for the high-performance and hardware-interacting aspects. C is sometimes used as an intermediate language by implementations of other languages.

   C (programming language) - Wikipedia

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

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   What is a library in C?

   • In C, a library is a set of functions contained within a single "archive" file. Each library typically has a header file, which contains the prototypes of the functions contained within the library that may be used by a program, and declarations of special data types and macro symbols used with these functions.

   C (programming language) - Wikipedia

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

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

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

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   2 days 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.

6. epn.org › what-are-the-functions-of-function-keysWhat are the functions of function keys in keyboard? - EPN

   epn.org › what-are-the-functions-of-function-keys

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   1 day ago · The Functions of Function Keys: 1. F1: Help. F1 is commonly used as the help key. Pressing it typically opens a help menu or brings up contextual help within a program or application. 2. F2: Rename. The F2 key is often used to rename files or folders in operating systems like Windows.

7. ticktocktech.com › blog › 2024/05/26Computer Keyboard Key Explanations - What do these keys do?

   ticktocktech.com › blog › 2024/05/26

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   1 day ago · What are the function keys on a computer keyboard? The function keys on a computer keyboard are the keys labeled F1 through F12. Each of these keys typically performs a specific function depending on the software or operating system being used. For example: – F1: Often opens help. – F2: Generally used to rename a selected item.

8. www.geeksforgeeks.org › what-are-toggle-keysWhat are Toggle Keys? - GeeksforGeeks

   www.geeksforgeeks.org › what-are-toggle-keys

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   5 days ago · A toggle key switches input from other keys on the keyboard between two different modes. The most frequent toggle key is Caps Lock, which switches the letter keys between lowercase and uppercase modes.

9. www.geeksforgeeks.org › how-to-fixdict_keys-objectHow to Fix”dict_keys’ object is not subscriptable” in Python

   www.geeksforgeeks.org › how-to-fixdict_keys-object

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   3 days ago · The error message “dict_keys’ object is not subscriptable” in Python typically occurs when try to access an element of the dictionary using the square brackets[ ] but we are attempting to do so on a dict_keys object instead of the dictionary itself.