C++ :: Allocation / Deallocation Of Array Within Struct
Feb 27, 2013
Okay so I have a question. Lets say I want to create arrays of exact size for abstract data type members. For example:
struct student {
char name[10];
int idNumber;
};
My question is how to declare this array as null so that later i can give it an exact size to match the length of the name. if it were not a part of the struct i would imagine that the code would look something like this:
I need to confirm that this problem cannot be solved without a pointer. Namely I need to read the rows and columns number from the user cin >> m, n and then use to declare an array int A[m][n];
However as m and n are not constants I am not able to do that. Is there a workaround? The following is the solution I came with BUT using a pointers which should be not the case.
// solution with using pointers as "int A[m][n]" does not work for me!!! void TwoDimensionalArrayFunc(){ int m = 0; int n = 0;
// instruct the users to enter array dimensions cout << "Please insert value for m:"; cin >> m;
I have a 1000 bytes global array (which did not dynamic allocated).
I need to make "dynamic allocation" from this array.
For example - MyMalloc(50) ---> The program will allocate 50 bytes OF THE ARRAY'S SIZE. ------ MyFree(pointer) ---> I need to check if the pointer is in the array and free the space.
It should be managed by blocks. The array should also contain the manage variables (for me).
What are the exact differences in these two types of methods of allocating memory for an array ? When does 1st method is useful and when does 2nd ?I also read somewhere that in Ist method memory is allocated from heap but i don't know from where memory is allocated in 2nd method and what difference these memory allocations causes.
class Base { }; class Derived1 : public Base { }; class Derived2 : public Base { } class Bar { public: void SomeFunc();
[code].....
MSVC2010 throws out compiler error which says:
Code:
no operator found which takes a right-hand operand of type 'Derived *' (or there is no acceptable conversion)
What I don't understand is why? The pointer is an address of 0 element of an array. So what is the problem? I can eliminate the error by using double pointer but it will be an overkill.
I coded a program that takes some strings and lexicographically orders the strings and its substrings. I have used dynamic memory allocation technique and its working fine for all strings without consecutive same alphabets.I use a list in which a string is placed in its exact position by moving the others right.
When I run the program this is the output: Amy Adams 10111 97 86 78 95
-842150451 -6.27744e+066 -6.27744e+066 -6.27744e+066 -6.27744e+066 and so on .....
Press any key to continue . . .
As you can see the program is reading the first students information and outputting that fine, but the rest of the students have bad values for output. I'm guessing it's something to do with the pointer, but I really can't figure it out, why it won't read all of the students info?
I have three questions concerning the below code I have written, which is expected to do basically as the attached diagram illustrates:
Code: #include <stdio.h> #include <stdlib.h> double getAverageGrade(int studentGrades[] , int size); int* getStudentInfo(int * numCourses); int main()
[Code] ...
(1) How may I display the averages to 2 decimal places, namely why doesn't %.2lf work? The program gives 89.00 for 89 and 90, for instance. (2) How may I read the number of courses and the relevant grades in a row for each student? (3) How may I free (de-allocate) my array of pointers, namely grades? Does it suffice to use free(grades)?
I was doing a side programming challenge in my workbook that asked me to dynamically allocate and array for test scores. So far I have an array that will accept an integer to allocate the amount of test scores and then will accept integers to populate the array, however when I try to cout the contents of the array the numbers are absurdly different than what was put in. Here's my code:
#include "stdafx.h" #include <iostream> using namespace std; void main() { cout << "How many test scores?" << endl; int scores(0);
[Code] ....
And this is the output screen: How many test scores? 4 Enter test score 1: 22 Enter test score 2: 33 Enter test score 3: 44 Enter test score 4: 55 -33686019 18472 55656634 201345063 Press any key to continue . . .
Why am I getting these crazy numbers? I've looked back and forth from examples in my book and it doesn't look like I'm doing anything wrong.
Suppose I wished to reallocate memory (resize) an array of pointers. Why does the following not work?(The program runs, yet yields a faulty segmentation error message. Why?):
I'm now working on a class to handle matrices and matrix operations. I dynamically allocate a two dimensional array with its size as an input. My problem is that i need to resize the matrix structure (to fit to the size of a product of two matrices or to adjust the size after deleting a row or column for example). I make the resizing by deleting the allocated 2d array after saving its first element address to another pointer to pointer, after saving the useful data in an other array, then i use new[] operator to create a new 2d array using the same address of the old deleted array.
void My_matrix ::delete_row(int a) { int i,j; int buffer_row_index = -1; //note that our work is zero based, as we acess the private member of an object of the same class we are working on and we access to the array as it is (zero based) so if this variable is -1, it will be 0 when it enters for the first time and saves the data in the right position. My_matrix buffer(number_of_rows-1,number_of_columns);
[Code] ....
I do this in a way that i think is unsafe. This code is sometimes unstable and gives an unhandled exception whose reason is unknown. I need to know whether this way is good enough or if there any other better ways.
Dynamic memory allocation in array in c programming. I am trying to make the user to choose the size of array they want to engage in the game.
However, i have remove the global variable which contribute the error to my code previously. Now I assigned all the arr individually but not using the global variable. However, i still not get the desired board i want. i still keep getting 9x9 array board.
And i also need limit the board size only from 4 to 9. And how do i do that.
I'm a little lost with this program. The idea is to dynamically allocate an array and increase its size every time a new integer is inputted by the user. I believe it is a memory leak but as we have just started learning this I'm not sure how to recognise it. Sometimes I can input as many integers as I want other times 2 or 3 before it crashes. When I can input enough values i exit the loop and send it to the sort function and mean calculator function, all works fine there except the last number inputted becomes this huge value not hexadecimal though... As such I'm at a loss as what to look at next, so here you go:
I wrote this simplified version of a program i am writing that parses data in UDP packets. In the process of doing so i pretty much answered all my questions and fix all the problems i was having.
decodeSystemMap function will be in loop, and will proccess packets that have mostly the same data, only a few items will be added or changed or deleted.
whats the best way to check if there are any new, deleted, or removed items in the packet and only modify those? Is there anything unsafe / dangrous about the way the code is now?
Code: /* * File: main.c * Author: david * * Created on May 23, 2013, 11:57 AM */
I am working on an assignment identical to another post from a couple years ago, for reference here is the thread:
array of pointers to structures sorting addresses by zip code
They way it is written on that thread is almost identical to the way the teacher implied to have it done (only wrote part of the input block). But I am having an error:
When it gets to the output section it outputs then next name along with the zip code... I tried strncpy and strxfrm but both cause more problems than they did work.
The last part of the project is to have the output put out in order of least zip code to most zip code (00000<99999), so this is causing me a real problem and I do not see what exactly is making this happen.
Here is my code (we dont HAVE to use gets but professor suggested using it for this assignment, next lab is to rewrite this using files and fgets rather than I/O redirection):
I have not started the sorting code because I cannot get past this, but once I have proper zip codes I am sure I can make a sort function no problem.
I am using xcode with some breaks to read variables as various points and do not notice anything wrong until it makes it to the output functions, although this page briefly pops up between input and output functions when the breaks are up:
I am trying to pass a struct through an array to another array from one microprocessor to another microprocessor and then dereference that array to update the same exact struct on the other microprocessor.My goal is to always have values inside of both structs while sending any updates to the struct on the other microprocessor in the mean time but I seem to be looping through the data and the members of the struct seem to be cleared out after every clock cycle. I can verify this by the flashing of my leds which the struct controls.
It doesn't make sense to me why this is working. The way my mind is thinking about this is that vertices is an array of type VertexPos, so then why can it be initialized with objects of type XMFLOAT3?
What I'm trying to do with this code is an address book and I have an array of pointers which are returned by malloc whenever I need to add an extra entry in the address book. What I need to do is search for a specific entry using bsearch. I've got an inqSort() function that sorts the table and runs normally, but my program crashes when I try to use bsearch.
Every time an entry is inserted, I inqsort() the array so it's always sorted, and it works as expected. But when I try to call findEntryUI(); from the main() function, the program crashes after entering the name I want to search.
I have to search an array of struct students on the basis of their first names, last names and roll numbers .. so far i am done with the input of the student first , last names and roll numbers . I have problem in searching the array ..
I basically just want a function that tells me if 'X' or 'O' won in a tic-tac-toe game. I don't care about the visuals, I just want a function that tells me if 'X' or 'O' won. If X wins, return 0. If Y wins, return 1.
How to do the diagonals, but as far as the across and down wins, I know I have to use a nested for loop, but am a little stuck, as to exactly how to set it up.
struct Speaker { static int numElem; string name; int number; // Phone string topic; float fee; };
// IN main() FUNCTION Speaker s[10];
The goal is for numElem to keep track of how many of the 10 elements are in use. However, I'm not sure the proper way to access the element, if it's even possible.
I want to delete selected records from struct array using cstring reading from files. Here I read my records to stud struct then assign non-deleted to stu struct but its not deleting as desired...strcmp is giving 25
while(cont=='Y'){ cout<<"Enter student ID to delete: "; cin.ignore(); cin.getline(id, 15,
[Code] ....
I did some debugging effort and I found here is the problem..the stud[0].ID and id is not same but why? I am giving in same id and both char array lenght is 15
while(cont=='Y'){ cout<<"Enter student ID to delete: "; cin.ignore(); cin.getline(id, 15); cout<<strlen(stud[0].ID)<<" "<<strlen(id)<<endl;///---> lenght 1 is 10 ///---->lenght 2 is 8 cout<<strncmp(id,stud[0].ID, 10 )<<endl;
