C++ :: Filling Dynamically Allocated Array With Values
Jan 12, 2013
Just trying to fill a dynamically allocated array with values then I want to print out the values using pointer method:
#include <iostream>
using namespace std;
long * extend_arr(long int arr[], long int length, long int val) {
long * array2 = new long [length + 1];
for (int J = 0; J < length; ++J)
array2[J] = arr[J];
[Code] ....
When this runs, I get an array with random numbers in it. For example, just trying to print the first value in *Block gives me random numbers each time. What is wrong with this as to why it is not holding the right values?
The extend_arr works perfectly fine, because when I try to access the values in the array using indexes (arr[0], arr[1], etc) it shows the right output, but using pointers does not. How can I make it work?
this is my function for allocating memory in 2D array
Code:
#include <stdio.h> #include <stdlib.h> int allocate_array(int **array, int *row, int *column){ int i; }
[code]....
end of allocate_array function and this is my function for asking for the values to be stored in array
Code:
int input_array(int **array, int row, int column){ int i, j; //ask for the values to be stored in the 2D array for( i = 0; i < row; i++ ){ for( j = 0; j < column; j++ ){ }
[code]....
why I'm having error here in my input_array() function
I have changed my const global int NUMLABS to a non constant variable so that the user can decide how many labs to input. I adjusted the parameters of each function to add NUMLABS becuase the variable is no longer constant. But now main() returns 0 right after the user chooses how many stations to put in each lab. I am having difficulty understanding these dynamically allocated arrays.
This program uses dynamic arrays to store login information for four labs. Each of the four labs is referenced by the labs[] array which is indexed from 0-3. A pointer in the labs[] array then references a dynamic array that is of size for however many computers are in that lab.
Written by: Luca Del Signore Last modified on: October 3rd Known bugs: N/A *********************************************************************/ #include <iostream> #include <cstdlib> using namespace std;
Suppose I wished to initialize a dynamically allocated array of integers to zero. Would I do better to use calloc() or malloc + iterate over all entries setting each to zero? Which one is regarded as a better approach?
void readFile(struct course *d, char* filename){ FILE* fp; char buffer[100]; int i = 0, array_size = 100; struct course *temp;
[code]....
I will be using this to read data from a file. I start with an array of 100 structures being passed to the readfile function. Once it reads 100 lines (i == array_size), I want to double the array size until I have finished reading the file.
Two questions.
1)My initial thought was that I needed to keep track of the lines read with my variable, i. However, is there a better way?
2)My program is crashing right now at the call to double_array_size function. What is wrong with my code? Never dealt with dynamically allocated array of structures and functions.
I read online that I should change my code in the following manner.
I can paste the "error messages" if you like, but it is a page full of stuff I have never seen. glibc detected, Backtrace, Memory Map, and a bunch of numbers and hexadecimal stuff like addresses.
I'm trying to read in a file and store it in an array that is dynamically allocated of a struct (which I'm not sure how to do), then parse each line using strtok() from string.h. The idea is to separate the lines by date, subject, time, etc.
Since the array is a dynamically allocated of typdef struct, it's sorted by the date of each struct, with an intial size of 25. But whenever the array needs to be resized, it should be doubled.
This a very simple program I created because I dont understand how do this. My goal is to be able to use the pointer *s5 throughout the program. For example I would to like to call other functions and pass that pointer through the function. I understand the dynamic allocation and pointers for the most part but Im confused here because the "new char[20]" variable will die after the function and I dont want it to.
#include <iostream> #include <cstdlib> #include <cstring> using namespace std; void testArray ( char *s5 ); int main ( int argc, char *argv[] )
In a program I'm working on now, i need a milti-dimensional array. To save space, I used dynamically allocated array by using pointers, something like this-
int *arr; arr=new int[col*row];
And now i need to pass this array in a function. What are the parameters in the function declaration statement and at the function call statement?
I'm trying to write a function that returns a pointer to a dynamically allocated array. Here's my code:
#include <iostream> using namespace std; void IndexArray(int, int); int main(){ int *arr, n;
[Code] ....
When I try running the program, I get the error
"Unable to start program 'D:C++FilesdynamicArraySolReleasedynamicArray.exe'. The system cannot find the file specified."
I'm honestly not sure if the issue is my program, or something with C++. At the moment, I cannot debug any of my programs or else I get the same exact error. I basically need to release everything without debugging it. I last used C++ about a year ago and I'm finally back in school, and so trying to get back into it. I use Microsoft Visual C++ 2010.
I'm trying extremely hard to understand pointers and I have the basic concept down.. I feel as though my knowledge of dynamically allocated pointers and pointers in general is not enough to understand the logic behind what I'm trying to do. The problem is that the donations array must be able to accept any number of donations. I've made it do just that, but there is also an array of pointers which must each point to the same element in the donations array. The program works if I assign int *arrPtr[100] for example, but it does not work if I try to dynamically allocate it to accept the same number of elements for donations entered by the user. Here it's the snippet
#include <iostream> using namespace std; //Function Prototypes
I am trying to store each value of a column from a text file into an dynamically allocated array, which needs to be globally declared for further usage in the program.The input textfile contains the following:
#include<stdio.h> #include<stdlib.h> #include<string.h> int main() }
[code]....
The commented printf line gives the entire values of the column, which proves that the file is correctly being read.But on compiling this program I get both compiler warnings and finally segmentation fault.
Having some frustrating issues trying to free memory from a dynamically allocated array of pointers to linked lists. I think the problem is in how I initialize the pointers to NULL. Is there a more elegant way to have the program recognize that the list is empty so it knows to create a head node for the linked list in the function 'add_end_stub_to_array'?
I ran the code through Valgrind and it says that memory is definitely lost from this array.
This is the structure definition.
Code: struct stub_edge { int loc_id; int anim_type; int mkt; struct stub_edge *next_node; };
Here is the code snippet from main allocating and deallocating memory to the array.
Here the function for adding nodes to the lists by reading through a dynamically allocated 2D array. (The end_stubs array is ordered by month and each linked list represents events occuring within the month).
Code:
struct stub_edge **add_end_stub_to_array(int **end_stubs, struct stub_edge **list) { long int i = 0; int mon = 0; struct stub_edge *current_node1; struct stub_edge *new_node1; int break1 = 0; while(i < num_edges && break1 == 0 && mon < 12)
[Code]...
Here is the function for freeing memory from the list.
I have the following dynamically allocated 2D array:
Code:
int num_rows = 100; int num_cols = 3; double **myArray= (double**)malloc( sizeof(double *) * num_rows); for(i = 0; i < num_rows; i++) { myArray[i] = (double*)malloc( sizeof(double) * num_cols); }
After sorting the array based on the values in column 1,:
Code:
qsort(myArray, num_rows, sizeof(myArray[0]), comp_function); int comp_function(const void* a, const void* b) { double **p1 = (double**)a; double **p2 = (double**)b; double *arr1 = *p1; double *arr2 = *p2;
return arr1[0] - arr2[0]; }
I need to split the array into two halves so that I can pass each separately into another function that accepts a type double ** pointer. What is the most efficient way of splitting the array? Is it possible to keep the original double ** pointer for the first half of the array and then assign a new double ** pointer to the second half of the array?
When I first learned about dynamically allocated arrays in school, I always thought we used them for passing arrays as parameters to functions. But the more I have been practicing coding, I see now that normal arrays can be passed as parameters to functions. So, what is the advantage? Why do we even need them?
I am trying to delete these arrays NumArray1.array and NumArray2.array at the end of my program so that there is not a memory leak. However I always get a double free or corruption error in runtime error with delete[] array_name. I have tried many times to use nullptr, but no matter what my compiler does not recognize it as being declared in the scope of my delete function. (I have commented out the that function for now.)
What is also strange about this is that I can perfectly use delete[] a1.array, which corresponds to NumArray1.array, but any of the other times I have tried to use the command, it has always resulted in syntax or runtime errors. Online resources do not adequately explain this scenario, though I am sure it exists elsewhere. all of my attempted solutions have failed, and I am completely at a loss. how to free the dynamically allocated arrays at the end of my program?
#include <iostream> #include <assert.h> using namespace std; // Define a struct type, each struct type variable has three // member variables: array, capacity, and length. Togther these // three variable represent a partially filled array.
I understand why you cant define them but why cant you name them. Or is it that you must always define them in order to name them?
Why do I have to always use a pointer???
Or is it that dynamically allocated variables on allocate space for a type to be stored and not really the variable itself so you must use a pointer???
How to diagnolize a matrix that can be of any size (obviously has to be square)
I have written the code and have all basic operators overloaded to handle any size matrix, including +, =, * (mat*mat), *(scalar), -, <<, >> and and overloaded = operator that copies over the result to a new matrix.
#include <stdio.h> int main(void) { //2D Array int array[2][2]; int number = 1; }
[code]....
The array is not filled incorrectly for some reason, more specifically the first row.The first two cycles of the for loop seem to work correctly. One if the bugs seems to occur on the third. when array[0][2] is filled with number 7, for some reason array[1][0] changes it value to 7 as well.
Code: int arr2d[rows][columns] ; // Not valid syntax of course ... let be arr2d rows * columns size for(int i=0; i<rows; i++) for(int j=0; j<columns; j++) arr2d[rows][columns] = some_value;
What is the complexity? I believe O(n) and not O(n^2) on this case because if you have 3*3 size you would put 9 elements (from 9 elements input of course)... for each input you have one insertion and that is the meaning. Same as 4*4 size 16 input times 16 insertions .. or 5*5 and so forth...
