在static_assert（）中编译时显示整数 [英] Display integer at compile time in static_assert()

问题描述

以下是我正在尝试做的简化版

Here is a simplified version of what I'm trying to do

enum First
{
    a,
    b,
    c,
    nbElementFirstEnum,
};
enum Second
{
    a,
    b,
    c,
    nbElementSecondEnum,
};

static_assert(
    First::nbElementFirstEnum == Second::nbElementSecondEnum,
    "Not the same number of element in the enums.");
/*static_assert(  
    First::nbElementFirstEnum == Second::nbElementSecondEnum, 
    "Not the same number of element in the enums." + First::nbElementFirstEnum + " " + Second::nbElementSecondEnum);*/

但我希望能够打印First ::的值断言消息中的nbElementFirstEnum和Second :: nbElementSecondEnum（就像在注释版本中显然不起作用）。
我尝试使用＃进行宏连接。
我还尝试使用可变参数模板，使用％10检索每个数字并将0字符添加到检索到的值，但我得到的只是constexpr char []。

But I would like to be able to print the value of First::nbElementFirstEnum and Second::nbElementSecondEnum in the assert message (like in the commented version which obviously doesn't work). I have tryed using macro concatenation with "#". I also tryed using variadic templates, retrieveing with %10 each number and adding the '0' character to the value retrieved, but all I get is a constexpr char[].

所以我的问题是如何让我的枚举值以字符串文字打印。

So my question is how can I get my enums values to be printed in a string literal.

可能重复：

C ++ 11 static_assert：参数化错误消息

整合类型名称在static_assert输出？

最有趣的话题是这一个：
在编译时打印sizeof（T）
但我不想发出警告或退出代码来了解这些值。

The most interesting topic was this one: Printing sizeof(T) at compile time But I don't want to have a warning, or decomment code to know the values.

推荐答案

这基本上有效，但是只要稍微努力就可以打破（通过使V1和V2总和达到256的倍数）。所以，我认为你的解决方案更加丑陋但更强大。

This basically works, although it's possible to break with a little effort (by making V1 and V2 sum to a multiple of 256). So, I think your solution is uglier but still more robust.

template <int V1, int V2> struct AssertEquality
{
    static const char not_equal_warning = V1 + V2 + 256;
};

template <int V> struct AssertEquality<V, V>
{
    static const bool not_equal_warning = 0;
};

#define ASSERT_EQUALITY(V1, V2) static_assert( \
    AssertEquality<static_cast<int>(V1), \
                   static_cast<int>(V2)>::not_equal_warning == 0, \
    #V1 " != " #V2 );

// ...

ASSERT_EQUALITY(First::nbElementFirstEnum, Second::nbElementSecondEnum);

输出如下：

g++ -std=c++0x -c chksz.cpp
chksz.cpp: In instantiation of ‘const char AssertEquality<3, 2>::not_equal_warning’:
chksz.cpp:40:124:   instantiated from here
chksz.cpp:5:53: warning: overflow in implicit constant conversion
chksz.cpp:40:1: error: static assertion failed: "First::nbElementFirstEnum != Second::nbElementSecondEnum"

---

作为参考，这个原始版本依赖于gcc打印 static_assert 消息，即使布尔条件根本不编译也是如此。

---

For reference, this original version depended on gcc printing the static_assert message even when the boolean condition doesn't compile at all.

template <typename Enum1, int Max1, typename Enum2, int Max2>
struct AssertSameSizeEnums;

template <typename Enum1, int EnumMax, typename Enum2>
struct AssertSameSizeEnums<Enum1, EnumMax, Enum2, EnumMax> {};
// only define the special case where Max1 and Max2 have the same integer value

#define ASSERT_SAME_SIZE_ENUMS(E1, M1, E2, M2) static_assert( \
    sizeof(AssertSameSizeEnums<E1, E1::M1, E2, E2::M2>), \
    #E1 "::" #M1 " != " #E2 "::" #M2 );

enum class First {
    a, b, c, nbElementFirstEnum,
};
enum class Second {
    a, b, c, nbElementSecondEnum,
};

ASSERT_SAME_SIZE_ENUMS(First, nbElementFirstEnum, Second, nbElementSecondEnum);

注意我将您的枚举更改为强类型，因为否则枚举的常量名称会发生​​冲突。如果你有弱类型的枚举，传递给宏的第一和第二应该命名封闭的范围。

Note I changed your enums to be strongly-typed, because otherwise the enumerated constant names clashed. If you have weakly-typed enums, the First and Second passed to the macro should name the enclosing scope.

现在，如果我注释掉其中一个值（因此枚举的大小不同），我得到：

Now, if I comment out one of the values (so the enums are different sizes), I get:

g++ -std=c++0x -c chksz.cpp
chksz.cpp:25:113: error: invalid application of ‘sizeof’ to incomplete type ‘AssertSameSizeEnums<First, 3, Second, 2>’
chksz.cpp:25:1: error: static assertion failed: "First::nbElementFirstEnum != Second::nbElementSecondEnum"

查看完整值在不完整类型错误中的显示方式，以及静态断言中的符号名称？

See how the integer values are displayed in the incomplete type error, and the symbolic names in the static assertion?

这篇关于在static_assert（）中编译时显示整数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！