class point
{
private:
int* arr;
int len;
public:
point(int a)
:len(a)
{
arr = new int[len];
}
int& operator[](int a)
{
if (a<0 || a>=len)
exit(1);
else
return arr[a];
}
};
int main()
{
point p(3);
for (int i = 0; i < 3; i++)
p[i] = i;
return 0;
}
When I do this, the compilation works well
class point
{
private:
int* arr;
int len;
public:
point(int a)
:len(a)
{
arr = new int[len];
}
int operator[](int a)
{
if (a<0 || a>=len)
exit(1);
else
return arr[a];
}
};
int main()
{
point p(3);
for (int i = 0; i < 3; i++)
p[i] = i;
return 0;
}
When you do this,
p[i] = i;
In this part, the expression displays an error as lvalue that cannot be modified. I wonder why compilation errors appear if I don't attach a reference because of the reference next to int.
reference
int operator[](int a);
The code above is int in the form of the return value of the function.
Because the function returns by default by value, the int-type value is returned to the place where this function was called. In other words, p[i] returns an int-type number.
Therefore, the reason for the error in p[i]=i; is that int-type number is returned as a result of p[i]
Like number=i;, it became a code to substitute another number for a number, so the error "number is not lvalue" appeared.
int& operator[](int a);
On the other hand, if you add a reference (&) after the int as above, it means that the value you want to return is a declared variable (whether it has a name or not), and the place where the return value is sent (the called place) is a nickname for the already declared variable (the value you want to return). The question code returns the ath of the class's member variable, arr. Therefore, p[i]=i; is the nickname of arr[i]=i;.
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