Bit Fields

A bit field is a set of bits aligned within a single implementation defined storage unit called a word.
Everything about bit fields is implementation dependent.

struct {
    unsigned int is_keyword : 0;
    unsigned int is_literal : 0;
    unsigned int is_identifier : 0;
} text;

This struct¹ contains 3 bits called is_keyword, is_literal and is_identifier. However, due to padding, the size of this struct¹ is still 4.

References

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1. Read more about struct. ↩↩