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c++autofunction-templatestype-deductiontemplate-instantiation

type deduction failing for auto stdMaxInt = std::max<int>;

Using GCC 4.8.4 with g++ --std=c++11 main.cpp outputs the following error

error: unable to deduce ‘auto’ from ‘max<int>’
auto stdMaxInt = std::max<int>;

for this code

#include <algorithm>

template<class T>
const T& myMax(const T& a, const T& b)
{
    return (a < b) ? b : a;
}

int main()
{
    auto myMaxInt = myMax<int>;
    myMaxInt(1, 2);

    auto stdMaxInt = std::max<int>;
    stdMaxInt(1, 2);
}

Why does it work with myMax but not with std::max? And can we make it work with std::max?

Solution

  • It's because std::max is an overloaded function, so it doesn't know which overload you want to create a pointer to. You can use static_cast to select the overload you want.

    auto stdMaxInt = static_cast<const int&(*)(const int&, const int&)>(std::max<int>);