I want to achieve the following behaviour:
The code I have written is as follows:
#include<bits/stdc++.h>
using namespace std;
class DataSequence{
float *ptr;
int _size;
public:
DataSequence(float input[] , int size){
_size = size;
ptr = new float; ptr = input;
//print the array
cout << "Main constructor" << endl;
for(int i=0 ; i<_size; ++i){
cout << *(ptr+i) << " ";
// ++ptr;
}
}
//copy constructor
DataSequence(DataSequence &d){
_size = d._size;
ptr = new float; *ptr = *(d.ptr);
//print the array
cout << "copy constrructor" << endl;
for(int i=0 ; i<_size ; ++i){
cout << *(ptr+i) <<" ";
// ++ptr;
}
}
};
int32_t main(){
int size=4;
float input[size];
int bins;
input[0] = 3.4;
input[1] = 1.3;
input[2] = 2.51;
input[3] = 3.24;
DataSequence d(input , size);
cout << endl;
DataSequence d1 = d;
return 0;
}
The output is as follows
Main constructor
3.4 1.3 2.51 3.24
copy constrructor
3.4 2.42451e-038 -2.61739e-019 3.20687e-041
I am unable to figure out why I am getting garbage from the copy constructor, can someone help.
This statement:
ptr = new float;
only allocates a single float
. That means in this loop:
for(int i=0 ; i<_size; ++i){
cout << *(ptr+i)
as soon as i
is greater than 0, you dereference invalid memory, which is undefined behavior. This results in a program that can do anything, including producing the "garbage" output you see.
If you want to allocate an array, you need to do:
ptr = new float[_size];
and to delete it, you need to do:
delete [] ptr;
Note that even if you allocate memory correctly as shown above, you are not actually copying the data from the argument. Just setting pointers would do a shallow copy which is not what you want.
You can do a deep copy like this:
std::copy(d.ptr, d.ptr + _size, ptr);
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