AUTOSAR C++14 Rule A12-1-3

If all user-defined constructors of a class initialize data members with constant values that are the same across all constructors, then data members shall be initialized using NSDMI instead

Since R2021b

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Description

If all user-defined constructors of a class initialize data members with constant values that are the same across all constructors, then data members shall be initialized using NSDMI instead.

Rationale

You might be using user-defined class constructors to initialize the nonstatic data members of your class. When all user-defined constructors initialize nonstatic data members to the same value, using a user-defined constructor for initialization purposes is unnecessary. The best practice is to initialize the nonstatic data members directly in the class definition. Such in-class nonstatic data member initialization (NSDMI) enables you to use the error-free and efficient implicit constructor to obtain an instance of the class that has the data members initialized to a default values.

Polyspace Implementation

Polyspace flags a nonstatic data member declaration if either of these conditions is true:

  • The nonstatic data member is not initialized in-class and all user-defined constructors initialize the data member to the same value.

  • The nonstatic data member is initialized in-class and at the same time, it is also initialized in user-defined constructors.

This checker does not apply to:

  • Copy and move constructors

  • Union definitions

  • Arrays that are initialized in constructors

  • Objects that are initialized field by field in constructors

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

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#include <cstdint>
#include <string>
class MessageBox1
{
public:
	MessageBox1() : LowerLeft(0), UpperRight(0.0F), msg()
	{
	}
	// ...

private:

	int LowerLeft;     // Noncompliant
	float UpperRight;  // Noncompliant
	std::string msg;    // Noncompliant
};

class MessageBox2
{
public:
	// ...

private:
	int LowerLeft = 0;     // Compliant
	float UpperRight = 0.0F;         // Compliant
	std::string msg = "";   // Compliant
};
class MessageBox3
{
public:
	MessageBox3() : LowerLeft(0), UpperRight(0.0F), msg()
	{
	}
	

private:
	int LowerLeft = 0;      // Noncompliant 
	float UpperRight = 0.0F;          // Noncompliant
	std::string msg = "";    // Noncompliant 
};
class MessageBox4
{
public:
	MessageBox4() : LowerLeft(0), UpperRight(0.0F), msg()
	{
	}
	// ...
	MessageBox4(int int_i): LowerLeft(int_i),UpperRight(0.1F), msg("str"){}
private:

	int LowerLeft;     // Compliant
	float UpperRight;            // Compliant - Initialized differently in two c'tor
	std::string msg = "";//Noncompliant -  Initialized differently in two c'tor
};

In this example, Polyspace flags nonstatic data member initializations that violate this rule. For instance:

  • In class MessageBox1, the declarations of the data members are noncompliant because they are initialized by a user-defined constructor instead of by in-class initialization. The best practice is to declare such data members directly in-class and to use the default implicit constructors.

  • In class MessageBox2, the declarations of the data members are compliant because they are initialized directly in-class and the class defines no user-defined constructor.

  • In class MessageBox3, the declarations of the data members are noncompliant because they are initialized in-class while the constructor of the class also initialize the data members. The best practice is to declare the data members in class and omit a user defined constructor.

  • In class MessageBox4:

    • The declaration of AA::LowerLeft and AA::UpperLeft are compliant because two different constructors initialize them to different values and they are not initialized in-class.

    • The declaration of AA::msg is noncompliant because two different constructors initialize it to different value and it is also initialized in-class.

Check Information

Group: Special member functions
Category: Required, Automated
PQL Name: std.autosar_cpp14.A12_1_3

Version History

Introduced in R2021b

See Also

Topics