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Home Forums What does the explicit keyword mean? – MindStick
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1 Answers

Aryan Kumar
Aryan Kumar 10 Jul 2023
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In C++, the explicit keyword is used to prevent implicit conversions from one type to another. For example, the following code will compile without any errors:

C++

int main() {
  int x = 10;
  float y = x; // This is an implicit conversion
  return 0;
}

In this code, the integer x is implicitly converted to a float y. This is because the float type is considered to be "larger" than the int type.

However, if we use the explicit keyword, the implicit conversion will not be allowed:

C++

int main() {
  int x = 10;
  explicit float y = x; // This will not compile
  return 0;
}

In this code, the compiler will generate an error because the explicit keyword is used. This means that the conversion from int to float must be explicit.

The explicit keyword can be used with constructors, casts, and type conversion operators.

Here are some examples of how the explicit keyword can be used:

  • Constructors: The explicit keyword can be used with constructors to prevent implicit conversions from one type to another. For example, the following code will not compile:

C++

class MyClass {
  explicit MyClass(int x) {}
};

int main() {
  MyClass my_class(10); // This will not compile
  return 0;
}

In this code, the MyClass constructor is declared with the explicit keyword. This means that the constructor cannot be called implicitly. To call the constructor, we must explicitly cast the value 10 to a MyClass object.

  • Casts: The explicit keyword can also be used with casts to prevent implicit conversions from one type to another. For example, the following code will not compile:

C++

int main() {
  int x = 10;
  float y = static_cast<float>(x); // This will not compile
  return 0;
}

In this code, the static_cast operator is used to convert the integer x to a float y. However, because the static_cast operator is preceded by the explicit keyword, the conversion will not be allowed.

  • Type conversion operators: The explicit keyword can also be used with type conversion operators to prevent implicit conversions from one type to another. For example, the following code will not compile:

C++

class MyClass {
public:
  operator int() const { return 10; }
};

int main() {
  MyClass my_class;
  int x = my_class; // This will not compile
  return 0;
}

In this code, the MyClass class has a type conversion operator that converts a MyClass object to an int. However, because the type conversion operator is preceded by the explicit keyword, the conversion will not be allowed.

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