C語言struct中的長度可變數組(Flexible array member)

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C_struct中的長度可變數組(Flexible array member)

Flexible array member is a feature introduced in the C99 standard of the C programming language (in particular, in section §6.7.2.1, item 16, page 103). It is a member of a struct, which is an array without a given dimension, and it must be the last member of such a struct, as in the following example:

struct vectord {    uint8_t  len;    double   arr[]; // the flexible array member must be last};

• arr[]不佔用結構體的儲存空間，sizeof(strcut vectord)的值為1
• 變長數組必須是結構體的最後一個成員
• 結構體變數相鄰的連續儲存空間是arr[]數組的內容
• gcc中使用0長度的數組arr[0]來表示變長數組。

struct vectord *allocate_vectord (size_t len) {   struct vectord *vec = malloc(offsetof(struct vectord, arr) + len * sizeof(vec->arr[0]));   if (!vec) {       perror("malloc vectord failed");       exit(EXIT_FAILURE);   }   vec->len = len;   for (size_t i = 0; i < len; i++)       vec->arr[i] = 0;   return vec;}

C語言struct中的長度可變數組(Flexible array member)