有没有拿到警告行为不端的指定初始化的方法吗？ [英] Is there a Way to Get Warned about Misbehaving Designated Initializers?
问题描述
C99引入结构指定intializers的概念。因此，例如，给定的：
C99 introduced the concept of designated intializers for structs. So for example, given:
typedef struct {
int c;
char a;
float b;
} X;
我可以初始化，如：的printf（C =％d个\\ NA =％HHU \\ NB =％F，foo.c的，foo.a，foo.b）; 将输出：
C = 4结果
a = 1时搜索
B = 2.000000
c = 4
a = 1
b = 2.000000
<一个href=\"http://stackoverflow.com/questions/18731707/why-does-c11-not-support-designated-initializer-list-as-c99/29337570?noredirect=1#comment46864214_29337570\">As这里提到这已经分配给 C 那么的令人惊讶的行为 A 然后 b ，我的独立初始化指定的顺序。
As mentioned here this has the "surprising behavior" of assigning to c then a then b, independent of the order of my designated initializers.
这成为一个真正的问题，如果我有这样的功能：
This becomes a real issue if I have functions like this:
int i = 0;
int f() {
return ++i;
}
int g() {
i += 2;
return i;
}
int h() {
i += 4;
return i;
}
和我想初始化是这样的：的printf（C =％d个\\ NA =％HHU \\ NB =％F，foo.c的，foo.a，foo.b）; 我得到：
And I want to initialize like this: X foo = {.a = (char)f(), .b = g(), .c = h()}; Now when I do: printf("c = %d\na = %hhu\nb = %f", foo.c, foo.a, foo.b); I get:
C = 4结果
1 = 5结果
B = 7.000000
c = 4
a = 5
b = 7.000000
问题是有没有我的初始化顺序没有得到尊重的警告。是否有警告或东西，我可以启用此？
The problem being there was no warning that my initialization order was not respected. Is there a warning or something I can enable for this?
[活生生的例子]
推荐答案
的 ...没有任何警告，我的初始化顺序没有得到尊重的。
一个特定的初始化顺序的是基于其他的东西，然后在标准规定的期望。 （如在评论中指出）
A particular initialization order is an expectation based on something other then that stated in the standard. (as pointed out in the comments )
的 C99 的部分6.7.9，P23：23初始化列表前pressions的评价是indeterminately对于测序彼此，因此，
其中出现的任何副作用顺序的未指定的。
[重点煤矿]
C99 section 6.7.9, p23: 23 The evaluations of the initialization list expressions are indeterminately sequenced with respect to one another and thus the order in which any side effects occur is unspecified. [emphasis mine]
因此，有未定义除外（或未指定的）行为在这里没有问题。非常相似的其他C行为，如与函数参数的计算顺序的模糊性。
There is therefore no problem here except undefined (or unspecified) behavior. Very similar to other C behaviors such as the ambiguity with order of evaluation of function arguments.
修改的结果
C99有这样一段话有关：
EDIT
C99 has this to say about that:
从C99§6.5.2.2p10：结果
的函数参数的计算顺序是
未指定的的，功能指示器的评估的顺序，
实际参数中的实际参数，SUBEX pressions是
未指定的，但实际的呼叫前一个序列点。结果
[重点煤矿] 的
from C99 §6.5.2.2p10:
Order of evaluation of function arguments is unspecified, The order of evaluation of the function designator, the actual arguments, and subexpressions within the actual arguments is unspecified, but there is a sequence point before the actual call.
[emphasis mine]
的 在这里阅读更多 的
这是你preFER警告（你说好，+ 1）则是另一回事。我不知道这将是多么实用的是，虽然提供了警告 - 每 - - undefined- - 行为 - 在C / C ++语言。
That you would prefer a warning (which you stated well, +1) is another matter. I am not sure how practical it would be though to provide a warning for -every- -undefined- -behavior- in the C/C++ languages.
有趣的是需要注意的一些既定的假设/意见 <一个href=\"http://stackoverflow.com/questions/18731707/why-does-c11-not-support-designated-initializer-list-as-c99\">in这个讨论 的为什么C ++标准不包括指定初始化。 （然而）...
It is interesting to note some of the stated assumptions/opinions in this discussion why the C++ standards do not include Designated Initializers. (Yet) ...
... C ++更感兴趣的是把灵活性的一边
一种类型的设计师代替，因此设计人员可以很容易地使用
正确且难以键入错误使用。
...C++ is more interested in putting the flexibility on the side of the designer of a type instead, so designers can make it easy to use a type correctly and difficult to use incorrectly.
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