Yahoo Web Search

Search results

1. • • The following example creates a dictionary containing the atomic masses of some chemical elements. The element names are the keys and the masses are the values. The dictionary is a set of key:value pairs: In : atomic_mass = {'H': 1., 'C': 12, 'S': 32} Then we can add another key:value entry using: In : atomic_mass ['O'] = 16.
     csc.ucdavis.edu › ~chaos › courses

     Part C: Dictionaries, Arrays, Functions, and Modules - UC Davis

2. Top results related to what are the function of dictionary in c example list of elements with numbers

   • 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

     1/5

   • 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

     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 benefits / drawbacks of a list of lists compared to a numpy array of OBJECTS with regards to MEMORY?

     Top Answer

     Answered Nov 07, 2014 · 8 votes

     I'm going to answer your primary question, and leave the others (performance of transpose, etc.) out. So:

     I'm trying to understand the memory and other overhead implications that using numpy lists would have … Just to clarify I'm interested in the case where the numpy array type is object not a float, double or int

     A Python list is an array of pointers to Python objects wrapping whatever actual values you've stored in it—plus some extra slack to allow it to be expanded on the fly efficiently. Let's call that slack 20%, just for the sake of easy computation. For example, an list of 10000 32-bit integers takes up, say, 96000 bytes for the array, plus around 240000 bytes for the Python integer objects, plus a small overhead for the list itself, say 80 bytes again.

     A NumPy array is an array of whatever actual values you've stored in it. For example, an array of 10000 32-bit integers takes up 40000 bytes, plus a small overhead for the array itself, say 80 bytes. But when you're using dtype object, each "actual value" is just a pointer to a Python object, just as with a list.

     So, the only real difference here is the slack: The array is going to use 320080 bytes, while the list is going to use 336080 bytes. Not a huge difference, but it can matter.

     Also, does one become faster than the other in 2D vs ND or with the size along a given dimension.

     Yes, the nested list will increase faster… but not by a huge amount.

     A multidimensional array in numpy is stored as one giant array (in either C or Fortran striding order), so whether the shape is (10000,), (100, 100), or (10, 10, 10, 10), it's the same size. (The overhead may get a few bytes bigger to store more information about the striding, but if we're talking about, say, 256 bytes vs. 80 out of 320K, who cares?)

     A nested list, on the other hand, has more lists, with slack and overhead at every level. For example, a list of 10 lists of 10 lists of 10 lists of integers has 1+10+100+1000 arrays of 12 pointers, and 1+10+100+1000 list headers.

     So, the array is still using 320080 bytes, or maybe 320256, but the list is using 435536.

     If you want to know more about how list is implemented… well, that depends on the implementation you're using. But in CPython, the C API pretty much guarantees that it's going to be storing a contiguous array of PyObject *, and the fact that appending is amortized constant time pretty much requires that it leave slack that grows proportionately. And you can see in the headers and the source that this is exactly what it does. (Also, keep in mind that the specific sizes you get from that source will generally depend on the platform you compile it on. Most importantly, because there are pointers all over the place, 64-bit platforms tend to have somewhere between 50-100% more overhead per object for most objects than 32-bit platforms.)

     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

3. People also ask

   Can I create a dictionary in C?

   • You can create anything you want in C. You just won't have native language support for most of it. You can create a dictionary in C, but there is no dictionary built in to the standard C library. A quick search on Google code shows that there are open-source (and generously licensed) C dictionary implementations here and here.

   Do dictionaries exist in C? - Stack Overflow

   stackoverflow.com/questions/9405303/do-dictionaries-exist-in-c

   See all results for this question

   How do I create a dictionary?

   • Each dictionary has space for 1000 elements. You need add the files dic.c and dic.h in your project directory. After that you include dic.h create_dict: is a simple constructor for creating a dictionary and setting up the member field 'number_of_elements' and prepares the inner array 'elements'

   Algorithms_in_C: Dictionary

   thealgorithms.github.io/C/d1/d52/md_data__structures_2dictionary_2_r_e_a_d_m_e.html

   See all results for this question

   How do you count a list of elements?

   • First create a list of elements to count make an empty dictionary, we also do the same with lists create a for loop that will count for the occurrences of the "key", for each occurrence we add 1 if element in counts: counts[element] +=1

   python - Using a dictionary to count the items in a list - Stack Overflow

   stackoverflow.com/questions/3496518/using-a-dictionary-to-count-the-items-in-a-list

   See all results for this question

   What is an example of a function?

   • Examples of functions we have used include log ( ), sqrt ( ), abs ( ), cos ( ), etc. The "return type" indicates what kind of data this function will return. In the example above,the function returns an int. Some languages differentiate between "subroutines", which do not return a value, and "functions", which do.

   C Programming Course Notes - Functions - University of Illinois Chicago

   www.cs.uic.edu/~jbell/CourseNotes/C_Programming/Functions.html

   See all results for this question

4. www.geeksforgeeks.org › implementation-on-map-orImplementation on Map or Dictionary Data Structure in C

   www.geeksforgeeks.org › implementation-on-map-or

   • Cached

   Mar 27, 2023 · Last Updated : 27 Mar, 2023. C programming language does not provide any direct implementation of Map or Dictionary Data structure. However, it doesn’t mean we cannot implement one. In C, a simple way to implement a map is to use arrays and store the key-value pairs as elements of the array .

5. stackoverflow.com › questions › 75846950Dictionary Implementation in C with using arrays

   stackoverflow.com › questions › 75846950

   • Cached

   Mar 26, 2023 · C programming language does not provide any direct implementation of Map or Dictionary Data structure. However, it doesn't mean we cannot implement one. In C, a simple way to implement a map is to use arrays and store the key-value pairs as elements of the array.

6. csc.ucdavis.edu › ~chaos › coursesPart C: Dictionaries, Arrays, Functions, and Modules - UC Davis

   csc.ucdavis.edu › ~chaos › courses

   • Cached

   The following example creates a dictionary containing the atomic masses of some chemical elements. The element names are the keys and the masses are the values. The dictionary is a set of key:value pairs: In [1]: atomic_mass = {'H': 1., 'C': 12, 'S': 32} Then we can add another key:value entry using:

7. thealgorithms.github.io › C › d1Algorithms_in_C: Dictionary

   thealgorithms.github.io › C › d1

   • Cached

   c. Dictionary * create_dict (void); create_dict: is a simple constructor for creating a dictionary and setting up the member field 'number_of_elements' and prepares the inner array 'elements'. c. int add_item_label (Dictionary *,char label [],void *); add_item_label: adds item (void*) to the dictionary at given label returns 0 if adding was ...

8. www.cs.uic.edu › C_Programming › FunctionsC Programming Course Notes - Functions

   www.cs.uic.edu › C_Programming › Functions

   • Cached

   Function prototypes are often placed in separate header files, which are then included in the routines which need them. For example, "math.h" includes the function prototypes for the C math functions sqrt( ) and cos( ). Exercise: Write function prototypes for: A function which takes an int and a float, and returns a double.

9. www.freecodecamp.org › news › how-to-define-aDef in C – How to Define a Function in C - freeCodeCamp.org

   www.freecodecamp.org › news › how-to-define-a

   • Cached

   Apr 12, 2024 · For example, a user-defined function may calculate the sum of two numbers or check if a number is even or odd. In this article, you will learn how to create user-defined functions. Syntax of Functions in C. Here is the general syntax of a function in C: return_type function_name (parameter) { // function body with the code to be executed return ...

10. www.geeksforgeeks.org › sizeof-operator-csizeof operator in C - GeeksforGeeks

    www.geeksforgeeks.org › sizeof-operator-c

    • Cached

    May 6, 2023 · Example: C. #include <stdio.h> int main() { printf("%lu\n", sizeof(char)); printf("%lu\n", sizeof(int)); printf("%lu\n", sizeof(float)); printf("%lu", sizeof(double)); return 0; } Output. 1. 4. 8. Note: sizeof () may give different output according to machine, we have run our program on a 32-bit gcc compiler. 2.