How to make a copy constructor? - c++

Question

I want to make a copy constructor for this class RNA to copy the details form another object RNA
#include "RNA.h"
#include"Sequence.h"
#include<bits/stdc++.h>
using namespace std;
RNA::RNA()
{
set_sequence();
}
RNA::RNA(char * seq, RNA_Type atype)
{
int x;
int i=0;
while(1)
{
if(seq[i] != 'C'&&seq[i] != 'G'&&seq[i] != 'A'&&seq[i] != 'U')break;
x++;
i++;
}
x--;
length = x;
this->seq = new char[length];
for(int i=0;i<length;i++)
{
this->seq[i] = seq[i];
}
type = atype;
}
this is the copy constructor
RNA::RNA( RNA& rhs)
{
seq = new char[length];
for(int i=0;i<length;i++)
{
seq[i] = rhs.seq[i];
}
type = rhs.type;
}
in the main I try to do it and it make error
int l;
cin>>l;
char* arr = new char[l];
for(int i=0;i<l;i++)
{
cin>>arr[i];
}
cin>>l;
RNA anas(arr,(RNA_Type)l);
int s;
cin>>s;
char* arr2 = new char[s];
for(int i=0;i<s;i++)
{
cin>>arr2[i];
}
cin>>s;
RNA saeed(arr2,(RNA_Type)s);
saeed(anas); error is here
saeed.Print();
The error is " No match for call to '(RNA) (RNA&)'
so what can i do to solve this error

Answer 1

The simplest way is to let the compiler do it for you.
class RNA
{
RNA_Type type;
std::string seq;
public:
RNA(std::string = /* default seq */, RNA_Type = /* default type */);
/* implicitly generated correctly
~RNA();
RNA(const RNA &);
RNA & operator = (const RNA &);
RNA(RNA &&);
RNA & operator = (RNA &&);
*/
// other members
};
RNA::RNA(std::string aseq, RNA_Type atype)
: seq(aseq.begin(), aseq.find_first_not_of("ACGT")), type(atype)
{}

Answer 2

saeed already exists at that point, and you're trying to use it as if it were a function.
You can't copy-construct except when you are constructing, and it looks like any other initialisation:
RNA saeed(anas);
or:
RNA saeed{anas};
If you want to replace the value of an already existing object, you use assignment (and you need to implement that assignment; read about The Rule Of Three.)

Answer 3

The line
saeed(anas);
is not a call to the constructor RNA::RNA(RNA const&), but to RNA::operator()(RNA const&), which does not exist.
What you presumably want is a copy assignement operator
RNA& RNA::operator=(RNA const&);
which for simple enough classes will be auto-generated by the compiler (as explained in Caleth's answer). To call it, replace your line with
saeed = anas;