What's the difference between the two examples below?
Should I also assign the value inside the constructor in this class even though I have initialized?
Example 1:
class sof{
int teste;
public:
sof(int t) : teste(t){}
);
Example 2:
class sof{
int teste;
public:
sof(int t){
teste = t;
}
);
In this example it is indifferent since int does not have a default constructor. The construction is done directly by the compiler in the assignment. It would be different if the type of member to be initialized was a type that has a default constructor.
Let's think of something like this:
class Tipo {
int x;
public:
Tipo() {
x = 0;
}
Tipo(int p) {
x = p;
}
}
class sof {
Tipo teste; //chama o construtor padrão
public:
sof(int t) {
teste = Tipo(t); //chama o outro construtor
}
};
class sof {
Tipo teste; //não chama nada
public:
sof(Tipo t) : teste(t) {} //chama o construtor com parâmetro
};
This can be better checked in ideone or in CodingGround .
Note that if the default constructor does not exist, it has no option, the form of member initialization by list (the latter) is required.
I would like to complete the previous answer with the following code:
#include <iostream>
class Tipo {
int x;
public:
Tipo() {
x = 0;
std::cout << "tipo-default\n";
}
Tipo(int p) {
x = p;
std::cout << "tipo-int\n";
}
};
class sof {
std::ostream& x;
Tipo teste;
public:
sof(int t) : x(std::cout << "sof\n") {
std::cout << "sof-constr\n";
teste = Tipo(t);
}
};
int main() {
sof s(10);
return 0;
}
Here I show the case quoted by the previous answer and, furthermore, I show that the constructor of sof is not called in the execution of the class scope, but just before this constructor is called, as shown in the output: p>
sof
tipo-default
sof-constr
tipo-int
But it is also possible to see the other case of the member initializer lists which is the case of std::ostream& x : this must be declared and initialized in the "same statement" because it is a reference if it would be variables of type const ), then it can not be initialized in the constructor scope of sof .