Yahoo Web Search

Search results

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

   • 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

     Check all answers on Stack Overflow

     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.

     Check all answers on Stack Overflow

     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.

     Check all answers on Stack Overflow

     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.

     Check all answers on Stack Overflow

     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.

     Check all answers on Stack Overflow

     5/5

   Show moreShow less

2. www.geeksforgeeks.org › introduction-to-map-dataIntroduction to Map – Data Structure and Algorithm Tutorials

   www.geeksforgeeks.org › introduction-to-map-data

   • Cached

   May 1, 2024 · Map data structure (also known as a dictionary , associative array , or hash map ) is defined as a data structure that stores a collection of key-value pairs, where each key is associated with a single value.

3. www.geeksforgeeks.org › what-is-data-dictionaryWhat is Data Dictionary? - GeeksforGeeks

   www.geeksforgeeks.org › what-is-data-dictionary

   • Cached

   Apr 24, 2024 · Data dictionaries provide structured analysis and design tools by implementing data standards. Data standards are sets of rules that govern the collection, recording, and presentation of data. Using a data dictionary helps define the naming convention used in the model.

4. People also ask

   What is a dictionary & how does it work?

   • A dictionary is a kind of data structure that stores items in key-value pairs. A key is a unique identifier for an item, and a value is the data associated with that key. Dictionaries often store information such as words and definitions, but they can be used for much more.

   What Is A Dictionary In Python? | Simplilearn

   www.simplilearn.com/dictionary-in-python-article

   See all results for this question

   Why do you need a data dictionary?

   • Using a data dictionary helps define the naming convention used in the model. There are basically two types of data dictionaries in a database management system: Every relational database has an Integrated Data Dictionary available in the DBMS.

   What is Data Dictionary? - GeeksforGeeks

   www.geeksforgeeks.org/what-is-data-dictionary/

   See all results for this question

   What is a dictionary in Python?

   • A dictionary in Python is a collection of key-value pairs, where each key is associated with a value. It is an unordered data structure, and each key in the dictionary must be unique. Here is a dictionary example in Python: "name": "Alice", "id": 12345, "courses": ["Math", "Physics", "Chemistry"],

   Python Dictionary: Definition, Creation, Access, Deletion Examples

   diveintopython.org/learn/variables/dictionary

   See all results for this question

   What are data dictionaries?

   • Data dictionaries provide structured analysis and design tools by implementing data standards. Data standards are sets of rules that govern the collection, recording, and presentation of data. Using a data dictionary helps define the naming convention used in the model.

   What is Data Dictionary? - GeeksforGeeks

   www.geeksforgeeks.org/what-is-data-dictionary/

   See all results for this question

5. www.geeksforgeeks.org › hash-table-data-structureHash Table Data Structure - GeeksforGeeks

   www.geeksforgeeks.org › hash-table-data-structure

   • Cached

   5 days ago · A Hash table is defined as a data structure used to insert, look up, and remove key-value pairs quickly. It operates on the hashing concept, where each key is translated by a hash function into a distinct index in an array. The index functions as a storage location for the matching value.

6. guides.library.upenn.edu › cCodebooks & Data Dictionaries - Data Management Resources ...

   guides.library.upenn.edu › c

   Apr 29, 2024 · A good dictionary/codebook has enough information about each variable for it to be self explanatory and interpreted properly by someone outside of your research group. The terms are often used interchangeably, but codebooks tend to for survey data and allow the reader to follow the structured format of the survey and possible response value.

7. diveintopython.org › learn › variablesPython Dictionary: Definition, Creation, Access, Deletion ...

   diveintopython.org › learn › variables

   • Cached

   May 3, 2024 · Dictionary of Dictionaries. Dictionary of Objects in Python. Reverse of Keys and Values in Dictionary. Python provides several built-in collection types to store and manipulate data. Some of the commonly used collection types in Python are: Lists. Tuples. Sets. Dictionaries. Arrays. Deques.

8. www.simplilearn.com › dictionary-in-python-articleDictionary In Python [Made Easy with Examples] - Simplilearn

   www.simplilearn.com › dictionary-in-python-article

   • Cached

   May 1, 2024 · Check out the example of how to create a dictionary using the dict () function: # empty dictionary. my_dict = {} # dictionary with integer keys. my_dict = {1: 'apple', 2: 'ball'} # dictionary with mixed keys. my_dict = {'name': 'John', 1: [2, 4, 3]} # using dict() my_dict = dict({1:'apple', 2:'ball'})

9. techbeamers.com › python-sort-a-dictionary-by-keyPython Sort a Dictionary by Key With Examples - TechBeamers

   techbeamers.com › python-sort-a-dictionary-by-key

   • Cached

   Apr 14, 2024 · Python Sort a Dictionary by Key With Examples. Last updated: Apr 14, 2024 11:35 am. By Soumya Agarwal. 8 Min Read. Welcome to this Python tutorial where we will explore different methods to sort a dictionary by its keys. Sorting dictionaries is a common task in programming, and Python provides multiple ways to achieve this.