c++ How to initialize char in constructor - c++

Question

#include <iostream>
using namespace std;
class MyClass
{
private :
char str[848];
public :
MyClass()
{
}
MyClass(char a[])
{
str[848] = a[848];
}
MyClass operator () (char a[])
{
str[848] = a[848];
}
void myFunction(MyClass m)
{
}
void display()
{
cout << str[848];
}
};
int main()
{
MyClass m1; //MyClass has just one data member i.e. character array named str of size X
//where X is a constant integer and have value equal to your last 3 digit of arid number
MyClass m2("COVID-19") , m3("Mid2020");
m2.display(); //will display COVID-19
cout<<endl;
m2.myFunction(m3);
m2.display(); //now it will display Mid2020
cout<<endl;
m3.display(); //now it will display COVID-19
//if your array size is even then you will add myEvenFn() in class with empty body else add myOddFn()
return 0;
}
I cannot use string because I'm told not to, therefore, I need to know how I can make it such that it displays the desired output

Answer 1

How to initialize char array in constructor?
Use a loop to copy element by element:
MyClass(char a[])
{
//make sure that sizeof(a) <= to sizeof(str);
// you can not do sizeof(a) here, because it is
// not an array, it has been decayed to a pointer
for (int i = 0; i < sizeof(str); ++i) {
str[i] = a[i];
}
}
Use std::copy from <algorithm>
const int size = 848;
std::copy(a, a + size, str);
Prefer std::copy over strcpy, if you have to use strcpy, prefer strncpy instead. You can give size to it, so it can help prevent errors and buffer overflows.
MyClass(char a[])
{
strncpy(str, a, sizeof(str));
}
Use std::array from the library. It has various advantages, for e.g you can directly assign it like normal variables. Example:
std::array<char, 848> str = {/*some data*/};
std::array<char, 848> str1;
str1 = str;

Answer 2

To copy a string you have to use std::strcpy, not str[848] = a[848].
str[848] = a[848] copy only one element, but in your case it's a mistake, becasue your array has indexes [0, 847].
Try
class MyClass
{
private :
char str[848];
public :
MyClass()
{
}
MyClass(char a[])
{
std::strcpy(src, a);
}
MyClass operator () (char a[])
{
std::strcpy(src, a);
}
void myFunction(MyClass m)
{
}
void display()
{
cout << str;
}
};