Why Doesn't C Support Anonymous Structs?

Anonymous Structs in C : Why the Absence?

C extends the capabilities of C with syntax enhancements like anonymous unions. However, anonymous structs, a feature extending this syntactic convenience, are conspicuously absent in the standard. What lies behind this decision?

Unlike anonymous unions which are supported in C, C does not provide anonymous structs. Consequently, C supports anonymous unions for compatibility but omits anonymous structs due to the absence of such a need for compatibility.

Moreover, the use of anonymous structs to represent a group of elements accessible via different names (e.g., .v[i], .x, .y, .z) can introduce undefined behavior in C . C prohibits writing to one union member (.v[1]) and subsequently reading from another (.y). While some code may follow this practice, it remains ill-defined.

C offers alternative solutions for such scenarios, as exemplified by the following struct:

struct vector3 {
  float v[3];
  float &operator[](int i) { return v[i]; }
  float &x() { return v[0]; }
  float &y() { return v[1]; }
  float &z() { return v[2]; }
};

In summary, C 's lack of anonymous structs stems from unnecessary compatibility considerations and the availability of alternative mechanisms to achieve similar effects, ensuring well-defined behavior in the language.

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