C++ Initialization Quiz

1. Which C++ Standard did add in-class default member initializers?

C++98 C++11 C++14 C++17

2. Can you use auto type deduction for non-static data members?

Yes, since C++11 No Yes, since C++20

3. Do you need to define a static inline data member in a cpp file?

No, the definition happens at the same place where a static inline member is declared. Yes, the compiler needs the definition in a cpp file. Yes, the compiler needs a definition in all translation units that use this variable.

4. Can a static inline variable be non-constant?

Yes, it's just a regular variable. No, inline variables must be constant.

5. What's the output of the following code:

struct S {
    int a { 10 };
    int b { 42 };
};
S s { 1 };
std::cout << s.a << ", " << s.b;

Output is: 1, 0 Output is: 10, 42 Output is: 1, 42

6. Consider the following code:

struct C {
    C(int x) : a(x) { }
    int a { 10 };
    int b { 42 };
};
C c(0);

Select the true statement:

C::a is initialized twice. The first time, it's initialized with 10 and then the second time with 0 in the constructor. C::a is initialized only once with 0 in the constructor. The code doesn't compile because the compiler cannot decide how to initialize the C::a member.

7. What happens when you throw an exception from a constructor?

The object is considered "created" so it will follow the regular lifetime of an object. The object is considered "partially created," and thus, the compiler won't call its destructor. The compiler calls std::terminate as you cannot throw exceptions from constructors.

8. What happens when you compile this code?

struct Point { int x; int y; };
Point pt {.y = 10, .x = 11 };
std::cout << pt.x << ", " << pt.y;

The code doesn't compile. Designators have to be in the same order as the data members in the Point class. The code compiles and prints 11, 10. The code compiles and prints 10, 11.

9. Will this code work in C++11?

struct User { std::string name = "unknown"; unsigned age { 0 }; };
User u { "John", 101 };

Yes, the code compiles in C++11 mode. The code compiles starting with C++14 mode. The code doesn't compile even in C++20.

10. Assume you have a std::map<string, int> m;. Select the single true statement about the following loop:

for (const pair<string, int>& elem : m)

The loop properly iterates over the map, creating no extra copies. The loop will create a copy of each element in the map as the type of elem mismatches. The code won't compile as a const pair cannot bind to a map.