Why Don't C 11 Designated Initializers Exist?

Designating the Absence of Designated Initializers in C 11

In the realm of programming, designated initializers found prominence in the C99 standard. These initializers allowed developers to assign values to struct members selectively, enhancing code readability and conciseness. However, a noticeable absence of these initializers emerged in the C 11 standard, prompting inquiries into the rationale behind this omission.

The C 11 standard committee has repeatedly deliberated on the inclusion of designated initializers, considering proposals to embrace the feature. However, the consensus remains a resounding rejection of such proposals. The committee believes that efforts to implement designated initializers have historically encountered insurmountable challenges.

Consider the following code snippet in C99:

struct Person
{
    int height;
    int weight;
    int age;
};

int main()
{
    Person p { .age = 18 };
}

This code assigns a value to the age member of the Person struct while leaving the other members uninitialized. C99 allows such selective initialization, but C 11 does not.

One of the primary reasons for the exclusion of designated initializers in C 11 stems from the unpredictable evaluation order of the initializers in C99. The standard vaguely describes this order as "indeterminately sequenced," leaving room for unexpected program behavior. For instance, if the initialization of the Person struct involved function calls with side effects, the order of execution could have unintended consequences, which the compiler would not necessarily flag.

In contrast, C has stringent requirements for initializer-list evaluation, ensuring that initializers are executed in the order they appear. Enforcing such an order would have required breaking compatibility with the previous C99 design, which the committee deemed unacceptable.

While the absence of designated initializers in C 11 may have initially drawn criticism, the limitations imposed on their inclusion in C 20 have addressed concerns about indeterminate behavior. The standardized evaluation order in C 20 provides developers with greater certainty and control over the initialization process.

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