????C99?н??е??????????δ???С???????????????????????????е????????????????????????????????????????????????а??????????С?????顣???????sizeof?????С????????????????檔???????????????????malloc??????涯??????????????????????????С???????????????????С??   — ????C????????

????????????????????????￡?


#include <stdio.h>
// ??????????????
typedef struct StType {
       int count;
       int item[0];
} StType;

int main()
{
       printf("sizeof(StType) = %d "?? (int)sizeof(StType));
       int val[4] = {3?? 1?? 2?? 3};
       StType *st = (StType*)val;
       for (int i = 0; i < st->count; i++)
                printf("%d value =%d "?? i?? st->item[i]);
       return 0;
}
 


????????????н?????￡?


sizeof(StType) = 4
0 value = 1
1 value = 2
2 value = 3


????????????????????item[0]????????????????????????malloc????new?????б????????????????


StType*st=(StType*)newchar[sizeof(StType)+100*sizeof(int)];
st.count=100;
delete[]st;


???????????????????100??item??StType???????????delete[]st;?????????檔

???????????????????Fleiblearray member????C89??????????C99??????????????????У?????C99????????????????????????0???飬???int item[0];?????????????????int item[]?????????Щ??????????????????????????int item[0]?????????????

?????????VC?б????????澯????????￡?


warning C4200: nonstandard extension used :zero-sized array in struct/union
Cannot generate copy-ctor orcopy-assignment operator when UDT contains a zero-sized array


??????????? C99??????“???????”??

????C89 ????漲???????С??????????????????????C99 ?У????????????????????????????????????????????????? C++ ??????й??????????? C99 ?????????????飬??????? C99 ?? C ????????

??????????????????????????????????????????????????????????鯔????????????????????С??

??????????????????????????????????????????????????б??C89???????????????????м????????????????

????1??????1


struct header {
         size_t len;
         unsigned char data[1];
};
ptr = malloc(sizeof(struct header) + (n -1));


??????????????????Ч??????????????????????????????

????2??????2


struct header*my_header = malloc(offsetof(struct header?? data)
+ n * sizeof(my_header->data));


??????????ú?????????


#define FLEXIBLE_SIZE SIZE_MAX // or whatever maximum length for an array
#defineSIZEOF_FLEXIBLE(type?? member?? length)
(offsetof(type??member) + (length) * sizeof((type*)0)->member[0])


?????????????????????????????C89?????????????????????????????????????C99????????????????????????

????3??????3

????????????????????μ????????????????????????????