在使用模板时初始化数组 [英] Initializing arrays when using templates

问题描述

假设我有 Foo 类。以下工作正常：

Let's say I have the class Foo. The following works fine:

class Foo
{
    public:
        const int* bar;

        Foo()
        {
            bar = new int[2] {1, 2};
        }
};

但是，我试图稍微改变一下使用模板：

However, I tried to change this very slightly to use a template:

template<int A, int B>
class Foo
{
    public:
        const int* bar;

        Foo()
        {
            bar = new int[2] {A, B};
        }
};

我对模板工作方式的理解是 A 和 B 本质上是编译时常数，所以它应该仍然工作相同。

My understanding of the way templates work is that A and B are essentially compile time constants, so it should still work the same.

错误消息I编译 g ++ （链接中为4.5，与4.6.3出现同一错误）时得到的是：

The error message I get when compiling with g++ (4.5 in the link, same error with 4.6.3) is:

错误：ISO C ++禁止在数组中初始化new [-fpermissive]

error: ISO C++ forbids initialization in array new [-fpermissive]

使用4.7 会出现类似错误，但略有不同：

With 4.7 a similar error occurs, though slightly different:

错误：数组中的括号初始化器new [-fpermissive]

error: parenthesized initializer in array new [-fpermissive]

模板函数，而不仅仅是在大括号中使用模板参数进行初始化时，代码和输出。 （感谢Philipp）

The problem also occurs in template functions, and not just when template parameters are used within the braces for initialization, code and output. (thanks Philipp)

推荐答案

看起来这是一个GCC错误。 Clang接受它，标准允许它：

Looks like this is a GCC bug. Clang accepts it, and the standard allows it:

new-initializer： b

（ expression-list _opt ）

braced-init-list

( expression-list_opt)
braced-init-list

此初始化的规则不是特殊的：

And the rules for this initialization are not special:

创建 T 类型的对象初始化
对象，如下所示：

A new-expression that creates an object of type T initializes that object as follows:

如果省略 new-initializer ，则对象为
默认初始化（8.5）;如果不执行初始化，
对象具有不确定的值。

— If the new-initializer is omitted, the object is default-initialized (8.5); if no initialization is performed, the object has indeterminate value.

- 否则，新的初始化器是
根据8.5的初始化规则对直接初始化进行解释。

— Otherwise, the new-initializer is interpreted according to the initialization rules of 8.5 for direct-initialization.

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