C ++错误:没有匹配的函数来调用'print_size' [英] C++ error: no matching function for call to 'print_size'

问题描述

我有此代码:

#include <iostream>
#include <vector>

template<typename T>
void print_size(std::vector<T> a)
{
    std::cout << a.size() << '\n';
}

int main()
{
    std::vector<int> v {1, 2, 3};
    print_size(v);

    auto w = {1, 2, 3};
    // print_size(w); // error: no matching function for call to 'print_size'
                      // candidate template ignored: could not match 'vector' against 'initializer_list'
}

...它将编译并运行，没有任何问题.但是，如果启用注释行，则会产生错误no matching function for call to 'print_size'.

...which compiles and runs without any issues. But if I enable the commented-out line, it produces the error no matching function for call to 'print_size'.

我想知道用C ++ 11和更高版本编写此代码的正确方法是什么.

I would like to know what is the correct way to write this code in C++11 and later versions.

推荐答案

对于auto w = {1, 2, 3};，w的类型将为std::initializer_list<int>，并且print_size(w);失败，因为无法推导模板参数T. 模板参数推导不考虑隐式转换.

For auto w = {1, 2, 3}; the type of w will be std::initializer_list<int>, and print_size(w); fails because template parameter T can't be deduced; template argument deduction does not consider implicit conversions.

类型推导不考虑隐式转换(上面列出的类型调整除外):这是超载解析的工作，稍后会发生.

Type deduction does not consider implicit conversions (other than type adjustments listed above): that's the job for overload resolution, which happens later.

您可以显式指定模板参数

You can specify template argument explicitly,

print_size<int>(w);

或者您也可以将w设置为std::vector<int>；如果您坚持使用auto，则需要明确指定类型.

Or you can make w to be a std::vector<int> instead; and if you persist using auto you need to specify the type explicitly.

auto w = std::vector<int>{1, 2, 3};
print_size(w);

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