c - How does Lua UTString ensure maximum alignment for strings? -


i'm reading lua's (5.3.0) source code, , in lobject.h found using strange method manipulate string follow:

/*  ** header string value; string bytes follow end of structure  ** (aligned according 'utstring'; see next).  */  typedef struct tstring {      commonheader;      lu_byte extra;  /* reserved words short strings; "has hash" longs */      unsigned int hash;      size_t len;  /* number of characters in string */      struct tstring *hnext;  /* linked list hash table */ } tstring;   /* ** ensures address after type aligned. */ typedef union utstring {     l_umaxalign dummy;  /* ensures maximum alignment strings */     tstring tsv; }utstring;   /*  ** actual string (array of bytes) 'tstring'.  ** (access 'extra' ensures value 'tstring'.)  */ #define getaddrstr(ts)  (cast(char *, (ts)) + sizeof(utstring)) #define getstr(ts)  \ check_exp(sizeof((ts)->extra), cast(const char*, getaddrstr(ts)))

i have found answer reason of using such method in there. wondering ensures maximum alignment strings, mean? why need maximum alignment , how ensure?


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