How Does C 11 Handle In-Class Initialization Without Linker Conflicts?

C 11's In-Class Initialization Expansion: Breaking the Linkage Barriers

In C 03, in-class initialization was restricted to static const members of integral or enumeration types. This limitation stemmed from concerns about violating linker rules that require unique definitions for objects.

However, C 11 significantly relaxes these restrictions, allowing in-class initialization of non-static and non-const members. This raises the question of how the potential complications with linking have been addressed.

Contrary to initial intuition, the linker's operation remains largely unchanged. Instead, the compiler assumes the responsibility of handling the in-class initializations. It accomplishes this by ensuring that only one definition is generated for the class members, even if they are initialized within the class.

This change does introduce additional complexities for the compiler, but the impact on the programmer is generally minimal. One caveat arises when a class member has multiple initializers. In such cases, the compiler determines which initializer takes precedence based on the specific constructor used.

For example, consider the following class:

class X { 
    int a = 1234;
public:
    X() = default;
    X(int z) : a(z) {}
};

When creating an object using the default constructor, the value of 'a' is initialized to 1234. However, if a constructor that explicitly specifies a value for 'a' is used, the in-class initialization is disregarded.

X x{5678};

In this instance, the value of 'a' in the 'x' object will be 5678. This behavior ensures that the class member is always initialized to the most appropriate value, even in the presence of multiple initializers.

Overall, the expansion of in-class initialization capabilities in C 11 provides greater flexibility and convenience for programmers without compromising the integrity of the overall linking process.

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