# Extra Clang Tools 13 documentation

## clang-tidy - cppcoreguidelines-prefer-member-initializer

# cppcoreguidelines-prefer-member-initializer

Finds member initializations in the constructor body which can be converted into member initializers of the constructor instead. This not only improves the readability of the code but also positively affects its performance. Class-member assignments inside a control statement or following the first control statement are ignored.

This check implements C.49 from the CppCoreGuidelines.

If the language version is C++ 11 or above, the constructor is the default constructor of the class, the field is not a bitfield (only in case of earlier language version than C++ 20), furthermore the assigned value is a literal, negated literal or `enum` constant then the preferred place of the initialization is at the class member declaration.

This latter rule is C.48 from CppCoreGuidelines.

Please note, that this check does not enforce this latter rule for initializations already implemented as member initializers. For that purpose see check modernize-use-default-member-init.

## Example 1

    class C {
      int n;
      int m;
    public:
      C() {
        n = 1; // Literal in default constructor
        if (dice())
          return;
        m = 1;
      }
    };

Here `n` can be initialized using a default member initializer, unlike `m`, as `m`’s initialization follows a control statement (`if`):

    class C {
      int n{1};
      int m;
    public:
      C() {
        if (dice())
          return;
        m = 1;
      }

## Example 2

    class C {
      int n;
      int m;
    public:
      C(int nn, int mm) {
        n = nn; // Neither default constructor nor literal
        if (dice())
          return;
        m = mm;
      }
    };

Here `n` can be initialized in the constructor initialization list, unlike `m`, as `m`’s initialization follows a control statement (`if`):

    C(int nn, int mm) : n(nn) {
      if (dice())
        return;
      m = mm;
    }

UseAssignment

  If this option is set to true (default is false), the check will initialize members with an assignment. In this case the fix of the first example looks like this:

    class C {
      int n = 1;
      int m;
    public:
      C() {
        if (dice())
          return;
        m = 1;
      }
    };