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使用默认参数的 C++ 函数模板

转载 作者:塔克拉玛干 更新时间:2023-11-02 23:52:37 27 4
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#include <iostream>
#include <vector>
#include <string>
#include <cstring>
#include <functional>
using namespace std;

template <typename Object, typename Comparator>
const Object &findMax(const vector<Object> &arr,
const Comparator &isLessThan = less<Object>())
{
int maxIndex = 0;

for (int i = 1; i < arr.size(); i++) {
if (isLessThan(arr[maxIndex], arr[i])) {
maxIndex = i;
}
}
return arr[maxIndex];
}

int main()
{
vector<string> arr(3);
arr[0] = "ZED";
arr[1] = "alli";
arr[2] = "crocode";
//...
cout << findMax(arr) << endl;
return 0;
}

当我用g++编译时,出现如下错误:

test4.cpp: In function ‘int main()’:
test4.cpp:48:24: error: no matching function for call to ‘findMax(std::vector<std::basic_string<char> >&)’
test4.cpp:48:24: note: candidate is:
test4.cpp:10:15: note: template<class Object, class Comparator> const Object& findMax(const std::vector<Object>&, const Comparator&)

最佳答案

模板参数不能从默认参数推导出来。 C++11,[temp.deduct.type]§5:

The non-deduced contexts are:

  • ...
  • A template parameter used in the parameter type of a function parameter that has a default argument that is being used in the call for which argument deduction is being done.
  • ...

您可以使用重载来解决这个问题:

template <typename Object, typename Comparator>
const Object &findMax(const vector<Object> &arr, const Comparator &isLessThan)
{
int maxIndex = 0;

for (int i = 1; i < arr.size(); i++) {
if (isLessThan(arr[maxIndex], arr[i])) {
maxIndex = i;
}
}
return arr[maxIndex];
}

template <typename Object>
const Object &findMax(const vector<Object> &arr)
{
return findMax(arr, std::less<Object>());
}

关于使用默认参数的 C++ 函数模板,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/18980781/

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