调用模板类中的模板函数 [英] Calling template function within template class

问题描述

免责声明：以下问题可能很容易，我可能会震惊看到第一个答案。此外，我想为任何重复的问题道歉 - 句法问题并不总是很容易识别语言解释，因此搜索他们不是那么容易...

Disclaimer: The following question probably is so easy that I might be shocked seeing the first answer. Furthermore, I want to apologize for any duplicate questions - syntactic problems are not always easy to identify be verbal explanation and thus searching for them is not as easy...

但是足够的。我有一个两个模板化的类，其中一个有模板成员函数，其他类试图调用该函数。一个最小的错误产生示例如下所示：

But enough of that. I have a two templated classes, one of those has a templated member function, the other class attempts to call that function. A minimal, error producing example is shown below:

#include <iostream>

template <typename T>
class Foo {
public:
    Foo() {
    }

    template <typename outtype>
    inline outtype bar(int i, int j, int k = 1) {
        return k;
    }

};

template <typename T>
class Wrapper {
public:
    Wrapper() {
    }

    double returnValue() {
        Foo<T> obj;
        return obj.bar<double>(1,2); // This line is faulty.
    }

};

int main() {
    Wrapper<char> wr;
    double test = wr.returnValue();
    std::cout << test << std::endl;
    return 0;
}

在编译时，这会导致

At compile time, this results in

expected primary-expression before 'double'
expected ';' before 'double'
expected unqualified-id before '>' token

其中所有错误消息都指向代码中标记的链接。

where all error messages are directed at the linke marked in the code.

我已经谢谢你的想法，不管它们有多明显。

I allready thank you for your ideas, no matter how obvious they are.

推荐答案

obj.bar<double>(1,2); // This line is faulty.

此处需要模板关键字 obj 是 Foo 类型的实例，其中取决于模板参数 T ，因此上面应该写成：

The template keyword is required here, as obj is an instance of a type Foo<T> which depends on the template parameter T, and so the above should be written as:

obj.template bar<double>(1,2); //This line is corrected :-)

阅读@ Johannes的答案这里详细解释：

Read @Johannes's answer here for detail explanation:

• 在哪里和为什么我必须把模板和类型名称依赖名称？

• Where and why do I have to put "template" and "typename" on dependent names?

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