我知道这个问题很老了,但是在C++20最终将此特性从C带到C++之前,有一种方法可以解决它。您可以使用预处理器宏和static_asserts来检查初始化是否有效。(我知道宏通常很糟糕,但在这里我看不到其他方法。)请参见下面的示例代码:
#define INVALID_STRUCT_ERROR "Instantiation of struct failed: Type, order or number of attributes is wrong."
#define CREATE_STRUCT_1(type, identifier, m_1, p_1) \
{ p_1 };\
static_assert(offsetof(type, m_1) == 0, INVALID_STRUCT_ERROR);\
#define CREATE_STRUCT_2(type, identifier, m_1, p_1, m_2, p_2) \
{ p_1, p_2 };\
static_assert(offsetof(type, m_1) == 0, INVALID_STRUCT_ERROR);\
static_assert(offsetof(type, m_2) >= sizeof(identifier.m_1), INVALID_STRUCT_ERROR);\
#define CREATE_STRUCT_3(type, identifier, m_1, p_1, m_2, p_2, m_3, p_3) \
{ p_1, p_2, p_3 };\
static_assert(offsetof(type, m_1) == 0, INVALID_STRUCT_ERROR);\
static_assert(offsetof(type, m_2) >= sizeof(identifier.m_1), INVALID_STRUCT_ERROR);\
static_assert(offsetof(type, m_3) >= (offsetof(type, m_2) + sizeof(identifier.m_2)), INVALID_STRUCT_ERROR);\
#define CREATE_STRUCT_4(type, identifier, m_1, p_1, m_2, p_2, m_3, p_3, m_4, p_4) \
{ p_1, p_2, p_3, p_4 };\
static_assert(offsetof(type, m_1) == 0, INVALID_STRUCT_ERROR);\
static_assert(offsetof(type, m_2) >= sizeof(identifier.m_1), INVALID_STRUCT_ERROR);\
static_assert(offsetof(type, m_3) >= (offsetof(type, m_2) + sizeof(identifier.m_2)), INVALID_STRUCT_ERROR);\
static_assert(offsetof(type, m_4) >= (offsetof(type, m_3) + sizeof(identifier.m_3)), INVALID_STRUCT_ERROR);\
当您拥有一个具有const属性的结构体时,您可以这样做:
struct MyStruct
{
const int attr1;
const float attr2;
const double attr3;
};
const MyStruct test = CREATE_STRUCT_3(MyStruct, test, attr1, 1, attr2, 2.f, attr3, 3.);
这有点不方便,因为你需要针对每个可能的属性数量编写宏,并在宏调用中重复类型和实例名称。而且你不能在返回语句中使用宏,因为断言是在初始化之后执行的。
但它确实解决了你的问题:当你改变结构体时,调用将在编译时失败。
如果你使用C++17,甚至可以通过强制相同类型来使这些宏更加严格,例如:
#define CREATE_STRUCT_3(type, identifier, m_1, p_1, m_2, p_2, m_3, p_3) \
{ p_1, p_2, p_3 };\
static_assert(offsetof(type, m_1) == 0, INVALID_STRUCT_ERROR);\
static_assert(offsetof(type, m_2) >= sizeof(identifier.m_1), INVALID_STRUCT_ERROR);\
static_assert(offsetof(type, m_3) >= (offsetof(type, m_2) + sizeof(identifier.m_2)), INVALID_STRUCT_ERROR);\
static_assert(typeid(p_1) == typeid(identifier.m_1), INVALID_STRUCT_ERROR);\
static_assert(typeid(p_2) == typeid(identifier.m_2), INVALID_STRUCT_ERROR);\
static_assert(typeid(p_3) == typeid(identifier.m_3), INVALID_STRUCT_ERROR);\