Need a C++ constructor to initialize each members of an array. how to give value for for each elements of an array declared as a class object according to the users input.
View 1 RepliesIs it generally better to initialize string data members as nullptr or as a zero-size array?
I can understand the former is superior from a memory-use perspective and also not requiring the extra allocation step. However, many string management functions will throw an exception - wcslen for instance - if you pass them a null pointer. Therefore I am finding any performance gained is somewhat wiped out by the extra if(pstString==nullptr) guards I have to use where it is possible a wchar_* may still be at null when the function is called.
There are two class.How can I initialize an array of different class in a constructor?
class Ticket{
private:
int ID;
[Code]....
I have to provide a no-argument constructor (Cinema();)to initialize the ticket array and give the right ticket ID.
I am currently practicing designing classes. In one exercise, I am trying to store 15 words in an array, and randomly print one (using the rand() functions and seeding it with crime. I have a header file, a respective .cpp file, and a main .cpp file. When I try to compile the code using g++ GuessWord.cpp UseGuessWord.cpp -o UseGuessWord, I get the following error in my constructor: expected primary-expression before ‘{’ token
Here is my code:
header file (GuessWord.h):
#ifndef GUESSWORD
#define GUESSWORD
#include <string>
using namespace std;
[code].....
What the best way to initialize a constructor in an array of objects?
Usually I declare an array of objects like so:
Code:
Car toyota[100];
Is this the only way I know to initialize a constructor of an array:
Code:
for (int i = 0; i < 100; i++)
{
toyota[i] = Car(x, y);
}
Is this the proper way?
If I have an array of some class, and that class has const members, is there some way I can call a custom constructor on elements of the array?
I can't seem to reinitialize an element in foos in the example below. A thread on stack overflow mentioned the copy constructor show allow it, but I get "no match for call to '(Foo) (Foo&)'" when I try it.
Code:
class Foo {
public:
Foo();
Foo(int x, int y);
[Code] .....
I need to create a method (constructor) to initialize a bigint to an int value you provide [0, maxint].
Example: bigint(128).
Here is my class:
#ifndef BIGINT_H
#define BIGINT_H
const int MAXINT = 500;
class bigint{
public:
bigint();
[Code] ....
So if the user inputs (4123 for example). How would I make 4 in size[0], 1 in size [1], 2 in size [2], etc. I don't even know where to start. Im guessing I would start with a for loop. It has to be an integer. I cant use a string yet.
I am versed in qsorting struct members within a struct instance, as in the example below:
Code:
#include <iostream>
#include <stdlib.h>
using namespace std;
struct item_database {
[Code]....
What I CANT do however is to sort an array of structs by one of its members. This is a complete different problem even if it sounds similar.
In other words, the problem is this; Say we have a struct:
Code:
struct item_database {
int key;
string token;
};
Then we declare an array of this struct in the heap:
Code: item_database *idptr = new item_database[700000]; and initialize its values.
How would one go about sorting this heap array of structs by its member function "token"?
I used the following call to qsort (standard library) and call to the compare function but it doesnt work:
Code:
qsort (idptr, 1000, sizeof(string), compare);
Code: int compare (const void* a, const void* b){
if (*(char*)a >= *(char*)b)
return 1;
else
return -1;
}
Or in more lamens terms say we have the following stuct instances:
Key: Token:
1 Hello
2 World
3 How
4 Are
5 You
Then I need those structs to order according to token (alphabetically, increasing or decreasing depending whats in our compare function).....
files.c
Code:
#include "include/types.h"
#include "include/gaussian.h"
#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
[Code]....
I need to access the members .name and .filename to allocate memory and copy strings in there.
Code:
files[count]->name=malloc(64);
files[count]->filename=malloc(64); SIGSEGV error
How to make the reference working?
Example :
Code:
struct x {
int v[4];
};
const x test = { 0, 1, 2, 3 };
Why can I do this? How does the compiler know to write to this in the proper way? I get that v would be contiguous. Does that have something to do with it?
I am trying to initialize an array of pointers to an array of characters, I can do it in 3 lines but I really want to do it in one line at the same time keeping the #define.
3 lines initialization (can compile)
======================
#define A 1
#define B 2
char row1[] = {A|B, B, A};
char row2[] = {B, A};
char *test[]= {row1, row2};
1 line initialization (failed)
===============================
char *test[] = { {A|B, B, A}, {B, A} }; // <- how do i do this??
I do not want this because it waste ROM space
=============================================
char test[][3] = { {A|B, B, A}, {B, A} };
imagine you have a world class. Than you have a tile class. Now, in the world class is a array with a lot of tiles and I want to initialize them with my imagination(For example I want a grass floor). But how I can do this, the array can only be create with the standard constructor. But it would be stupid and not very fast, that the tiles are first initialized with the standard constructor and than overridden to build the world. Whats the best way to initialize such a array ?
View 12 Replies View RelatedI am creating a class that has a private array on the heap with a constructor that takes the size of the array and initializes it on the heap. Later I have to make a deconstructor delete the space and print out free after.In my code, I was able to heap a private array and make a deconstructor, but I don't know how to take the size of the array and initialize it on the heap. My guess is this:
int* size = new int();
Also when you initialize size on the heap, don't you also have to delete it too? If so, where, in the code, do you do that? Here is my code so far.
Class Student {
private:
int size;
int* array = new int[size];
public:
Student(); // Constructor
~Student(); // Deconstructor
[code]....
How do you make a constructor that takes the size of the array and initializes it on the heap
Student::~Student()
{
delete[] array;
cout << "Free!" << endl;
}
We can initialize normal function prototype's parameters with zero like this:-
void output(float = 0.0, int = 0);
or
void output(int = 0, int = 0, double = 0.0);
But how do you do the same for a pointer array or simply an array?
Assume that second parameter has to be an array.
I have tried the following and it does not work:-
void output(float = 0.0, int = 0);
void output(float = 0.0, *int = 0);
void output(float = 0.0, int* = 0);
void output(float = 0.0, int[] = 0);
void output(float = 0.0, int []);
But if I skip the default declarations altogether, it works.
like:
void output(float, int []);
or
void output(float, int*);
how can I do it by explicitly writing zero, just like the first cases?
I'm a newbie to C++ and I am writing a code that searches strings and checks their value. I'm mostly working with if statements.
My code tends crash on Dev C++, even when I haven't recently saved any changes or compiled it, citing "memory access errors".
I recompiled in visual studio, and visual studio told me I have string out of bound errors.
My code is very long... but most of it is copy and pasted with slightly different conditions.
I believe the problem lies in how I initialize arr[4] ??
#include <cstdlib>
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
int main() {
cout << "Hall symbol -- generator matrix program" << endl;
// Setting up a data structure bc a normal array cannot handle the data for the spacegroups
[Code] ....
I somewhere read "You cannot initialize a structure like that at run time."
Example:
struct item_info {
char itemname[15];
int quantity;
float retail;
float wholesale;
[Code] ....
But if you want to assign values at run time then you have to do it manually like:
strcpy(item[0].itemname, "rice");
item[0].quantity = 10;
item[0].retail = 40;
item[0].wholesale = 30;
I tried in internet but am unable to know the differences. I want to know the difference between those two in terms of run time and compile time. Explanation required also for below one. Is this run time or compile time? How does we actually decide which is run time and which is compile time!
struct item_info {
char itemname[15];
int quantity;
float retail;
float wholesale;
//int quatityonorder;
[Code] ....
I've got an error saying that there is an access violation at 0x0000040 error no 0xC0000005
I've searched the net, saying the error may be due to an uninitialzed variable.I debugged the code, and found out that an object created from directx D3DXMATRIXA16 is uninitialized.With values ??,??,?? in each element
pMeshContainer->pBoneMatrices = new D3DXMATRIXA16[g_NumBoneMatricesMax];
here, pMeshContainer is a variable passed into a function called GenerateSkinnedMesh by pointer
GenerateSkinnedMesh(..., D3DXMESHCONTAINER_DERIVED *pMeshContainer)
Then in turn, GenerateSkinnedMesh is called within a callback from a DirectX9 API called
ID3DXAllocateHierarchy
Code:
class CAllocateHierarchy : public ID3DXAllocateHierarchy {
public:
STDMETHOD( CreateFrame )( THIS_ LPCSTR Name, LPD3DXFRAME *ppNewFrame );
STDMETHOD( CreateMeshContainer )( THIS_
LPCSTR Name,
[code]....
when the method CreateMeshContainer finished execution, the meshContainer is passed back to its parent like this
*ppMeshContainer = pMeshContainer;
The whole meshContainer stuff is stored persistently inside the frame root wrapped within a class called CMesh So in that process, I haven't initialized pBoneMatrices in anyways. But what and where is the best way to initialize an array of DirectX9 objects.
There is a function called
D3DXMatrixIdentity(&...);
But how can I initialize each one of them with this call?
Notice that pMeshContainer->pBoneMatrices does contain a valid address, despite the fact that the elements inside it are never initialized...
Code:
#include<stdio.h>
#include<string.h>
typedef struct test
{
char a[5];
char b[10];
}t;
[Code] ....
In Unix (HP-UX) and Linux, the output of above program will be:
t.a=Helloworld!
Instead of the value of t.a ,i.e, "Hello" only.
Why such output? And what is the trick here to print the only value of t.a.
I'm trying to put file data into members of a class. Remember to type in the file name you want to open. Cool feature right? I just had Dbase.txt so I chose that.
Fixed stuff in the .txt. Now I need to figure out why it only does 1 set and then ends.
#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <fstream>
using namespace std;
class INFO {
[Code] .....
Dbase.txt:
Bob
Guy
Programmer
M
9999.99
40
------------------
Little
Guy
Little Brother
M
0.0
3
------------------
The following:
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char *argv[]) {
int i;
int arr[3];
[Code] ....
Notice we didn't set a value for second index but it returns 0. Should I assume that when declaring an array with n values, those values will be initialized to 0 automatically or should I still initialize the array with all 0s doing something like this:
Code:
for(i=0;i<sizeof(arr);i++) {
arr[i]=0;
}
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?
View 12 Replies View RelatedI am trying to initialize a 2D char array of strings into POSIX shared memory to be shared between 3 other processes. There are plenty of tutorials on how to use a pointer to share a single string or an integer between processes, but I could find no examples on how to initialize 1D or 2D arrays using mmap(). I have posted what I have so far below. It is the first program, which creates the shared memory object and initialize the array char files[20][2][100] with the value files[0][0][0] = ' '. What is the proper method to initialize and share an array in C?
(program initializes shared memory object and array)
Code:
#include<fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <sys/mman.h>
int main (int argc, char *argv[]){
[Code] ......
I am trying to store data in a struct to be able to read it latter . have problems initializing this.
struct FoodAndDrink {
struct Food {
char* CannedGoods[2] = {
"Canned Spaghetti",
"Canned Tuna",
[code] .....
ok here is the question: Write a function that will initialize a double data array element to 0.0 ?
View 4 Replies View RelatedI have a two dimensional array , who's parameters are decided by the user . Hence i cannot initialize it . Now i want to take input for the first the row and then check some condition and then move on and take input for the next row.
View 6 Replies View RelatedGetting back into programming after a few years off and a bit rusty.
My question is: Is this going to initialize the size of the vector array's position and color properly?
#include <GLFW/glfw3.h>
#include <vector>
class TerrainClass {
private:
struct VertexType {
std::vector<float> position[3];
[Code]...