MISRA C++:2023 Rule 15.1.3

Conversion operators and constructors that are callable with a single argument shall be explicit

Since R2024b

Description

Rule Definition

Conversion operators and constructors that are callable with a single argument shall be explicit.

Rationale

Class constructors and conversion operators that are callable with a single argument of a fundamental type can be inadvertently invoked by the compiler to convert a fundamental type variable into the class. Such implicit conversion can occur in unexpected places, resulting in unexpected behavior. Declare constructors and conversion operators that are callable with a single argument of fundamental type as explicit.

Polyspace Implementation

Polyspace^® reports a violation of this rule if a constructor or conversion operator satisfies all these conditions:

• The constructor or operator has a single argument, or one argument that is not default initialized.

• The single argument or the argument that is not default initialized has a fundamental type, such as integral types, floating point types, and void types.

• The constructor or operator is not declared as explicit.

Troubleshooting

If you expect a rule violation but Polyspace does not report it, see Diagnose Why Coding Standard Violations Do Not Appear as Expected.

Examples

Constructor Callable with Single Argument Not Declared explicit

In this example, the class MyClass has a constructor that is callable with a single integer. in the function foo(), the call to func() converts the integer 5 to an object of type MyClass. Such an implicit conversion can result in unexpected results. Polyspace reports a violation.

#include <iostream>

class MyClass {
public:
	MyClass(int x) : value(x) { //Noncompliant
		std::cout << "Constructor called with value: " << value << std::endl;
	}

private:
	int value;
};

void func(MyClass obj) {
	std::cout << "Function called with MyClass object." << std::endl;
}

void foo() {
	func(5); // Implicit conversion from int to MyClass
	//...
}

Check Information

Group: Special member functions

Category: Required

Version History

Introduced in R2024b