I have made struct and now I need to create an array for the corresponding struct. Could anyone help me how to go about that? I have looked at stuff online and couldn't really understand it, so could anyone give me an example and explanation on how to create an array of a struct.
struct CANDIDATE{
string candiFN;
string candiLN;
int partyID;
int votes;
};
The same way you make any array. The following makes an array of length 5.
CANDIDATE foo [5];
Then you can fill it however you'd like
for (unsigned int i = 0; i < 5; ++i)
{
CANDIDATE temp("first", "second", 1, 2);
foo[i] = temp;
}
Or
for (unsigned int i = 0; i < 5; ++i)
{
CANDIDATE temp;
temp.candiFN = "first";
temp.candiLN = "second";
temp.partyID = 1;
temp.votes = 2;
foo[i] = temp;
}
Note that in C++ using a std::vector introduces more safety and flexibility to most applications.
std::vector<CANDIDATE> bar;
for (unsigned int i = 0; i < 5; ++i)
{
CANDIDATE temp("first", "second", 1, 2);
bar.push_back(temp);
}
You can simply do this:
struct CANDIDATE{
string candiFN;
string candiLN;
int partyID;
int votes;
}array[5];
//just add an array between } and ;
You can make an array of values
CANDIDATE foo[5];
or a pointer array
CANDIDATE* foo = new CANDIDATE[5];
The first goes in the stack, the second in the heap and need manual delete
Anyway consider of use std::vector
Related
below is my code which processes the payload[] array and store it's result on myFinalShellcode[] array.
#include <windows.h>
#include <stdio.h>
unsigned char payload[] = { 0xf0,0xe8,0xc8,0x00,0x00,0x00,0x41,0x51,0x41,0x50,0x52,0x51,0x56,0x48,0x31 };
constexpr int length = 891;
constexpr int number_of_chunks = 5;
constexpr int chunk_size = length / number_of_chunks;
constexpr int remaining_bytes = length % number_of_chunks;
constexpr int size_after = length * 2;
unsigned char* restore_original(unsigned char* high_ent_payload)
{
constexpr int payload_size = (size_after + 1) / 2;
unsigned char low_entropy_payload_holder[size_after] = { 0 };
memcpy_s(low_entropy_payload_holder, sizeof low_entropy_payload_holder, high_ent_payload, size_after);
unsigned char restored_payload[payload_size] = { 0 };
int offset_payload_after = 0;
int offset_payload = 0;
for (size_t i = 0; i < number_of_chunks; i++)
{
for (size_t j = 0; j < chunk_size; j++)
{
restored_payload[offset_payload] = low_entropy_payload_holder[offset_payload_after];
offset_payload_after++;
offset_payload++;
}
for (size_t k = 0; k < chunk_size; k++)
{
offset_payload_after++;
}
}
if (remaining_bytes)
{
for (size_t i = 0; i < sizeof remaining_bytes; i++)
{
restored_payload[offset_payload++] = high_ent_payload[offset_payload_after++];
}
}
return restored_payload;
}
int main() {
unsigned char shellcode[] = restore_original(payload);
}
I get the following error on the last code line (inside main function):
Error: Initialization with '{...}' expected for aggregate object
I tried to change anything on the array itself (seems like they might be the problem). I would highly appreciate your help as this is a part of my personal research :)
In order to initialize an array defined with [], you must supply a list of values enclosed with {}, exactly as the error message says.
E.g.:
unsigned char shellcode[] = {1,2,3};
You can change shellcode to be a pointer if you want to assign it the output from restore_original:
unsigned char* shellcode = restore_original(payload);
Update:
As you can see in #heapunderrun's comment, there is another problem in your code. restore_original returns a pointer to a local variable, which is not valid when the function returns (a dangling pointer).
In order to fix this, restore_original should allocate memory on the heap using new. This allocation has to be freed eventually, when you are done with shellcode.
However - although you can make it work this way, I highly recomend you to use std::vector for dynamic arrays allocated on the heap. It will save you the need to manually manage the memory allocations/deallocations, as well as other advantages.
You can't assign a char * to a char []. You can probably do something with constexpr but I'm suspecting an XY problem here.
I have a class array inside which I have declared an array its size and length. I am trying to merge two sorted arrays by creating the third array on the heap and both the sorted array will be merged on the third array. But whenever I create a new arr on heap the compiler gives me this error: request for member '..' in '..' which is of non-class type
class Array
{
public:
int A[10];
int length;
int Size;
};
void display(Array arr)
{
int i;
for(i=0;i<arr.length;i++)
{
cout<<arr.A[i]<<" ";
}
}
void Merge(Array *arr1,Array *arr2)
{
int i,j,k;
i=j=k=0;
int *arr3;
arr3=new int[10];
while(i<arr1->length && j<arr2->length)
{
if(arr1->A[i]<arr2->A[j])
arr3->A[k++]=arr1->A[i++];
else
arr3->A[k++]=arr2->A[j++];
}
for(;i<arr1->length;i++)
{
arr3->A[k++]=arr1->A[i];
}
for(;j<arr2->length;j++)
{
arr3->A[k++]=arr1->A[j];
}
}
int main()
{
Array arr1{{1,3,5,7},4,4};
Array arr2{{2,4,6,8},4,4};
Array *arr3;
arr3=Merge(&arr1,&arr2);
display(*arr3);
return 0;
}
The root cause of all your problems is that you use C-Style array with a magical size 10. Like in int A[10];. This is a major problem and should be avoided in C++.
Additionally, and the same, In C++ we usually do not use raw pointer for owned memories or newand such stuff.
Anyway. The design will never work, if the number of elements in both Array classes is greater then 5. Because then you will definitely get an out of bounds problem.
You must use a std::vector.
So, all bad. But I know that I will hear now, that the teacher said, no vector but new. The teacher should be fired or begin to teach C instead of C++.
Anyway again, I will fix the major bugs for you. But the sorting algorithm will work neither.
So,
If you want to return an Array, then change the signature of your function aand return an Array.
You do want to have a new Array, not new intes. So, please allocate a new Array instead.
Do not forget to release the newed Arrary at then end.
Set size and length of the new array.
Refactor your complete code.
Code example with some fixes:
#include <iostream>
class Array
{
public:
int A[10];
int length;
int Size;
};
void display(Array arr)
{
int i;
for (i = 0; i < arr.length; i++)
{
std::cout << arr.A[i] << " ";
}
}
Array* Merge(Array* arr1, Array* arr2)
{
int i, j, k;
i = j = k = 0;
Array *arr3 = new Array;
while (i < arr1->length && j < arr2->length)
{
if (arr1->A[i] < arr2->A[j])
arr3->A[k++] = arr1->A[i++];
else
arr3->A[k++] = arr2->A[j++];
}
for (; i < arr1->length; i++)
{
arr3->A[k++] = arr1->A[i];
}
for (; j < arr2->length; j++)
{
arr3->A[k++] = arr1->A[j];
}
arr3->length = arr1->length + arr2->length;
return arr3;
}
int main()
{
Array arr1{ {1,3,5,7},4,4 };
Array arr2{ {2,4,6,8},4,4 };
Array* arr3;
arr3 = Merge(&arr1, &arr2);
display(*arr3);
delete[]arr3;
return 0;
}
I'm currently trying to write a script so that I can add an item to the last index the array has an item in. For example, if I initialized an array int a[5] and a[0], a[1], a[2] all have something, then the integer would be added to a[3]Here is what I have :
int main(){
int a[5];
a[0] = 10;
a[1] = 20;
a[2] = 30;
for (int i = 0; i < 5; i++){
if (a[i] < 0){
a[i] = 40; //Just an example for what it would be like.
}
}
}
I can't help but feel that there is a better way to do this, maybe a different if condition. I want to know if there's another way to check if the next index is empty.
You could use an array index counter. Say, int counter = 0;
Use the counter as an index when you store integers to the array a, like a[counter] = 5 After you add an integer to your array, increment the counter, counter++.
This way you could make sure that the next value being added to the array is always added the way you described in the question
A few things to probably clear up what looks like a misunderstanding around what an array is:
When you declare an array say
int main()
{
int a[5];
for (int i = 0; i < 5; i++)
{
printf("a[%d] = %d", i, a[i]);
}
}
All elements in the array exist already. Namely, you can access a[0] ... a[4] without hitting an error. All values of the array have already been set implicitly and you can see this by seeing the output of the printf. Note that those are values that you haven't set yourself and will vary. If you're curious about why they vary, you can see this: Variable initialization in C++
To set those values explicitly, you can initialize all values in the array to 0 like so:
int main()
{
int a[5] = {0};
for (int i = 0; i < 5; i++)
{
printf("a[%d] = %d", i, a[i]);
}
}
or through use of a static initializer
int main()
{
int a[5] = {1, 2, 3, 4, 5};
for (int i = 0; i < 5; i++)
{
printf("a[%d] = %d", i, a[i]);
}
}
However because all values of the array already exist on creation, there isn't really such a state as "uninitialized array" in C++ as they are . The value of a[3] is either set implicitly or explicitly depending on how you created the array.
std::vector is a dynamically growing array, based on how much space you need. In order to have this effect, std::vector keeps track of how much of the array is "used" through use of a size variable. If you wanted to reimplement that to get an idea of how it might be done, you would probably want a class like:
class MyArray
{
public:
MyArray() : m_size(0)
{
}
void AddVal(int data)
{
if (m_size < 5)
{
m_array[m_size++] = data;
}
}
int GetSize()
{
return m_size;
}
private:
int m_array[5];
int m_size;
}
If you initialize the array to 0, you can check if the value is 0.
Initilize:
int array[5] = {0};
Check for 0:
array[4] == 0;
I am trying to allocate space for vector of vector but after allocation gdb showing null in pVectorTemp_ but showing size 2
#include <iostream>
#include<vector>
using namespace std;
int main( )
{
int index1 = 2;
int index2 = 2;
vector<vector<float>*>* pVectorTemp_ = NULL;
pVectorTemp_ = new vector<vector<float>*>();
pVectorTemp_->resize(index1);
for(unsigned int i=0 ;i< index1;i++)
{
vector<float>* pvecTemp = new vector<float>();
pvecTemp->resize(index2);
(*pVectorTemp_)[index1] = (pvecTemp);
}
return 0;
}
gdb :
(gdb) pvector pVectorTemp_
elem[0]: $2 = (std::vector<float, std::allocator<float> > *) 0x0
elem[1]: $3 = (std::vector<float, std::allocator<float> > *) 0x0
Vector size = 2
Vector capacity = 2
So Am i doing anything wrong?
Inside the for loop body, you have:
(*pVectorTemp_)[index1] = (pvecTemp);
But note that the index of the for loop is i (index1 is the upper bound).
So, I think you have a typo or bug, and you may want to use i (not index1) as index inside [...].
Note also that you have a signed/unsigned mismatch, since in the loop you have unsigned int as index, and you compare that with index1, which is a signed integer.
But, anyway, your code is uselessly complicated.
You don't need to allocate all these vectors on the heap with new.
Just use automatic ("stack") allocation, e.g.:
int main()
{
int index1 = 2;
int index2 = 2;
// Your original code is commented out:
//
// vector<vector<float>*>* pVectorTemp_ = NULL;
// pVectorTemp_ = new vector<vector<float>*>();
vector<vector<float>> vectorTemp;
// pVectorTemp_->resize(index1);
// Just consider calling push_back.
for (int i = 0; i < index1; i++)
{
// vector<float>* pvecTemp = new vector<float>();
// pvecTemp->resize(index2);
// (*pVectorTemp_)[index1] = (pvecTemp);
vectorTemp.push_back(vector<float>(index2));
}
// No need for return 0 in main().
// return 0;
}
See how the code gets simplified!
(Code without comments follows.)
int main()
{
int index1 = 2;
int index2 = 2;
vector<vector<float>> vectorTemp;
for (int i = 0; i < index1; i++)
{
vectorTemp.push_back(vector<float>(index2));
}
}
As a further improvement, assuming that your C++ STL implementation provides that, you may want to use emplace_back() instead of push_back(), to build the nested vectors:
// Instead of vectorTemp.push_back(vector<float>(index2));
//
vectorTemp.emplace_back(index2);
In this case, a vector of size index2 is built directly into the vectorTemp ("outer" vector) container, without temporaries.
You may want to read also this thread on StackOverflow for further details:
push_back vs. emplace_back
These are the things I can find.
vector<vector<float>*>* pVectorTemp1 = new vector<vector<float>*>(); // (1)(4)
pVectorTemp1->resize(index1);
for (int i=0 ; i < index1; i++) { // (2)
vector<float>* pvecTemp2 = new vector<float>(); /(4)
pvecTemp2->resize(index2);
(*pVectorTemp1)[i] = (pvecTemp2); // (3)
}
Variables that differ only by trailing underscore is asking for trouble.
unsigned adds nothing, except the risk of a signed/unsigned mistake
The index should be i not index1.
It would be better to use local variables rather than heap allocation and pointers, but that would change the code too much.
Change
(*pVectorTemp_)[index1] = (pvecTemp);
with
(*pVectorTemp_)[i] = (pvecTemp);
So Am i doing anything wrong?
Yes, you are doing something wrong:
using dynamically allocation when not needed
using unnecessary raw loops
Here's a simplified version:
int main( )
{
int index1 = 2;
int index2 = 2;
std::vector<std::vector<float>> pVectorTemp_
( index1
, std::vector<float>(index2) );
}
Live demo
Ok, so I'm quite new to C++ and I'm sure this question is already answered somewhere, and also is quite simple, but I can't seem to find the answer....
I have a custom array class, which I am using just as an exercise to try and get the hang of how things work which is defined as follows:
Header:
class Array {
private:
// Private variables
unsigned int mCapacity;
unsigned int mLength;
void **mData;
public:
// Public constructor/destructor
Array(unsigned int initialCapacity = 10);
// Public methods
void addObject(void *obj);
void removeObject(void *obj);
void *objectAtIndex(unsigned int index);
void *operator[](unsigned int index);
int indexOfObject(void *obj);
unsigned int getSize();
};
}
Implementation:
GG::Array::Array(unsigned int initialCapacity) : mCapacity(initialCapacity) {
// Allocate a buffer that is the required size
mData = new void*[initialCapacity];
// Set the length to 0
mLength = 0;
}
void GG::Array::addObject(void *obj) {
// Check if there is space for the new object on the end of the array
if (mLength == mCapacity) {
// There is not enough space so create a large array
unsigned int newCapacity = mCapacity + 10;
void **newArray = new void*[newCapacity];
mCapacity = newCapacity;
// Copy over the data from the old array
for (unsigned int i = 0; i < mLength; i++) {
newArray[i] = mData[i];
}
// Delete the old array
delete[] mData;
// Set the new array as mData
mData = newArray;
}
// Now insert the object at the end of the array
mData[mLength] = obj;
mLength++;
}
void GG::Array::removeObject(void *obj) {
// Attempt to find the object in the array
int index = this->indexOfObject(obj);
if (index >= 0) {
// Remove the object
mData[index] = nullptr;
// Move any object after it down in the array
for (unsigned int i = index + 1; i < mLength; i++) {
mData[i - 1] = mData[i];
}
// Decrement the length of the array
mLength--;
}
}
void *GG::Array::objectAtIndex(unsigned int index) {
if (index < mLength) return mData[index];
return nullptr;
}
void *GG::Array::operator[](unsigned int index) {
return this->objectAtIndex(index);
}
int GG::Array::indexOfObject(void *obj) {
// Iterate through the array and try to find the object
for (int i = 0; i < mLength; i++) {
if (mData[i] == obj) return i;
}
return -1;
}
unsigned int GG::Array::getSize() {
return mLength;
}
I'm trying to create an array of pointers to integers, a simplified version of this is as follows:
Array array = Array();
for (int i = 0; i < 2; i++) {
int j = i + 1;
array.addObject(&j);
}
Now the problem is that the same pointer is used for j in every iteration. So after the loop:
array[0] == array[1] == array[2];
I'm sure that this is expected behaviour, but it isn't quite what I want to happen, I want an array of different pointers to different ints. If anyone could point me in the right direction here it would be greatly appreciated! :) (I'm clearly misunderstanding how to use pointers!)
P.s. Thanks everyone for your responses. I have accepted the one that solved the problem that I was having!
I'm guessing you mean:
array[i] = &j;
In which case you're storing a pointer to a temporary. On each loop repitition j is allocated in the stack address on the stack, so &j yeilds the same value. Even if you were getting back different addresses your code would cause problems down the line as you're storing a pointer to a temporary.
Also, why use a void* array. If you actually just want 3 unique integers then just do:
std::vector<int> array(3);
It's much more C++'esque and removes all manner of bugs.
First of all this does not allocate an array of pointers to int
void *array = new void*[2];
It allocates an array of pointers to void.
You may not dereference a pointer to void as type void is incomplete type, It has an empty set of values. So this code is invalid
array[i] = *j;
And moreover instead of *j shall be &j Though in this case pointers have invalid values because would point memory that was destroyed because j is a local variable.
The loop is also wrong. Instead of
for (int i = 0; i < 3; i++) {
there should be
for (int i = 0; i < 2; i++) {
What you want is the following
int **array = new int *[2];
for ( int i = 0; i < 2; i++ )
{
int j = i + 1;
array[i] = new int( j );
}
And you can output objects it points to
for ( int i = 0; i < 2; i++ )
{
std::cout << *array[i] << std::endl;
}
To delete the pointers you can use the following code snippet
for ( int i = 0; i < 2; i++ )
{
delete array[i];
}
delete []array;
EDIT: As you changed your original post then I also will append in turn my post.
Instead of
Array array = Array();
for (int i = 0; i < 2; i++) {
int j = i + 1;
array.addObject(&j);
}
there should be
Array array;
for (int i = 0; i < 2; i++) {
int j = i + 1;
array.addObject( new int( j ) );
}
Take into account that either you should define copy/move constructors and assignment operators or define them as deleted.
There are lots of problems with this code.
The declaration void* array = new void*[2] creates an array of 2 pointers-to-pointer-to-void, indexed 0 and 1. You then try to write into elements 0, 1 and 2. This is undefined behaviour
You almost certainly don't want a void pointer to an array of pointer-to-pointer-to-void. If you really want an array of pointer-to-integer, then you want int** array = new int*[2];. Or probably just int *array[2]; unless you really need the array on the heap.
j is the probably in the same place each time through the loop - it will likely be allocated in the same place on the stack - so &j is the same address each time. In any case, j will go out of scope when the loop's finished, and the address(es) will be invalid.
What are you actually trying to do? There may well be a better way.
if you simply do
int *array[10];
your array variable can decay to a pointer to the first element of the list, you can reference the i-th integer pointer just by doing:
int *myPtr = *(array + i);
which is in fact just another way to write the more common form:
int *myPtr = array[i];
void* is not the same as int*. void* represent a void pointer which is a pointer to a specific memory area without any additional interpretation or assuption about the data you are referencing to
There are some problems:
1) void *array = new void*[2]; is wrong because you want an array of pointers: void *array[2];
2)for (int i = 0; i < 3; i++) { : is wrong because your array is from 0 to 1;
3)int j = i + 1; array[i] = *j; j is an automatic variable, and the content is destroyed at each iteration. This is why you got always the same address. And also, to take the address of a variable you need to use &