c++ - 数组初始化 [c/c++]

Question

为什么不允许这样做？

#include <cstdio>

struct Foo {
int fooId;
char arr[ ];
} fooList[] =
{ {1, {'a', 'b'}},
  {2, {'c', 'd'}}
};

int main()
{
  for (int i = 0; i < 2; i++)
    printf("%d %c\n", fooList[i].fooId, fooList[i].arr[0]);
}

然而，这是允许的:

struct Foo {
int fooId;
char arr[2]; // this line modified
} fooList[] =
{ {1, {'a', 'b'}},
  {2, {'c', 'd'}}
};

Answer 1

只有 C 结构的 last 成员可以像 arr[] 那样灵活。

无耻地抄袭 ISO C99 标准第 6.7.2.1 段第 16 段:

16 As a special case, the last element of a structure with more than one named member may have an incomplete array type; this is called a flexible array member. With two exceptions, the flexible array member is ignored. First, the size of the structure shall be equal to the offset of the last element of an otherwise identical structure that replaces the flexible array member with an array of unspecified length.106)...

编辑:

关于 C++，参见 this .底线:C++ 中根本不允许使用灵活的数组成员 - 至少目前是这样。