非静态成员初始化来自另一个非静态

Question

非常简单的问题。这个有效的C++ 11吗？

struct Foo { 
    int bar = 1; 
    int baz = bar; 
}; 

GCC（4.7.2）和锵（3.1）既与迂腐设置接受它：

-std=c++11 -Wall -W -pedantic

英特尔C++（13.0.1.117）没有。它在int baz = bar;与：

error: a nonstatic member reference must be relative to a specific object

谁是正确的？

万一你不知道，我用这个像这样的代码，它带来的初始化代码紧密联系起来，而不是最后一行移动到构造函数：

uint8_t colorR = -1; 
uint8_t colorG = -1; 
uint8_t colorB = -1; 
uint8_t colorA = -1; 
GLubyte RGBAVec[4] = {colorR, colorG, colorB, colorA}; 

Answer 1

5.1p12 An id-expression that denotes a non-static data member or non-static member function of a class can only be used:

• as part of a class member access (5.2.5) in which the object expression refers to the member’s class or a class derived from that class, or
• to form a pointer to member (5.3.1), or
• in a mem-initializer for a constructor for that class or for a class derived from that class (12.6.2), or
• in a brace-or-equal-initializer for a non-static data member of that class or of a class derived from that class (12.6.2), or
• if that id-expression denotes a non-static data member and it appears in an unevaluated operand.

所以，是的，这样的：

struct Foo { 
    int bar = 1; 
    int baz = bar; 
}; 

是有效的C++ 11。

但要小心约顺序，因为：

12.6.2p10 In a non-delegating constructor, initialization proceeds in the following order:

• First, and only for the constructor of the most derived class (1.8), virtual base classes are initialized in the order they appear on a depth-first left-to-right traversal of the directed acyclic graph of base classes, where “left-to-right” is the order of appearance of the base classes in the derived class base-specifier-list.
• Then, direct base classes are initialized in declaration order as they appear in the base-specifier-list (regardless of the order of the mem-initializers).
• Then, non-static data members are initialized in the order they were declared in the class definition (again regardless of the order of the mem-initializers).
• Finally, the compound-statement of the constructor body is executed

所以如在Non-static data member initializers proposal（问题3）指定：

A third issue is that class-scope lookup could turn a compile-time error into a run-time error:

struct S { 
    int i = j; // ill-formed without forward lookup, undefined behavior with 
    int j = 3; 
}; 

(Unless caught by the compiler, i might be intialized with the undefined value of j.)