Question

请考虑以下代码：

Unit& accessTree(std::string unitId2Find,  BSTree<Unit> &tree)
{
    Unit searchU;
    searchU.SetId(unitId2Find);
    return tree.search(searchU);
}

int main()
{
    using namespace std::placeholders;
    BSTree<Unit> tesTree;
    auto getUnit = std::bind(accessTree, _1, std::cref(tesTree));'

    Registration R;

..... //Setting required data

int i = R.GetCredits(getUnit); //Causes the error.

现在我尝试了两种不同类型的实现： 1

template<typename Fn>
unsigned Registration::GetCredits(Fn access)
{
    unsigned sum = 0;
    for(unsigned i = 0; i < GetSize(); i++)
        sum += results[i].GetCredits(access(results[i].GetUnit()));

    return sum;
}

template<typename Fn>
float Registration::CalculateGPA(Fn access)
{
    float total = 0;

    for (int i = 0; i < results.getLength(); i++)
    {
        total = total + results[i].GetGPAvalue() * results[i].GetCredits(access(results[i].GetUnit()));
    }

    return total / GetCredits(access);
}

2

unsigned Registration::GetCredits(Unit& (*access) (std::string & uId))
{
    unsigned sum = 0;
    for(unsigned i = 0; i < GetSize(); i++)
        sum += results[i].GetCredits(*access(results[i].GetUnit()));

    return sum;
}

float Registration::CalculateGPA(Unit& (*access) (std::string & uId))
{
    float total = 0;

    for (int i = 0; i < results.getLength(); i++)
    {
        total = total + results[i].GetGPAvalue() * results[i].GetCredits(*access(results[i].GetUnit()));
    }

    return total / GetCredits(func);
}

编译器： || === Build：在TesterProgram中调试（编译器：GNU GCC编译器）=== | E：\ CODE \ DSA \ TesterProgram \ BSTree.h ||在成员函数＆＃39; elemType＆amp; BSTree :: search（const elemType＆amp;）const [with elemType = Unit]＆＃39;： E：\ CODE \ DSA \ TesterProgram \ BSTree.h | 189 |警告：控制到达非空函数的末尾[-Wreturn-type] | E：\ CODE \ DSA \ TesterProgram \ src \ Regist.cpp ||在成员函数＆＃39; Vector＆amp;注册:: GetHighestResults（）＆＃39;：| E：\ CODE \ DSA \ TesterProgram \ src \ Regist.cpp | 100 |警告：引用局部变量＆＃39; vec＆＃39;返回[-Wreturn-local-addr] | E：\ CODE \ DSA \ TesterProgram \ src \ Regist.cpp ||在成员函数＆＃39; Vector＆amp;注册:: GetLowestResults（）＆＃39;：| E：\ CODE \ DSA \ TesterProgram \ src \ Regist.cpp | 125 |警告：引用局部变量＆＃39; vec＆＃39;返回[-Wreturn-local-addr] | .. \ TesterProgram \ vector.h ||在成员函数＆＃39; const T＆amp; Vector :: operator []（unsigned int）const [with T = Result]＆＃39;： .. \ TesterProgram \ vector.h | 277 |警告：控制到达非空函数的末尾[-Wreturn-type] | obj \ Debug \ main.o ||函数main':| E:\CODE\DSA\TesterProgram\main.cpp|81|undefined reference to unsigned int Registration :: GetCredits（std :: _ Placeholder＆lt; 1＆gt ;,std :: reference_wrapper const＆gt;））（std :: string，BSTree＆amp;）＆gt; ＆gt;（std :: _ Bind（std :: _ Placeholder＆lt; 1＆gt ;,std :: reference_wrapper const＆gt;））（std :: string，BSTree＆amp;）＆gt;）＆＃39; | || ===构建失败：1个错误，4个警告（0分钟，0秒（秒））=== |

这里发生了什么，我已经看过这个网站上的相关内容，但似乎没有什么能直接回答这个问题。

我不知道如何使用boost ::这是必需的，它将如何使用？

或者这是运行时/编译器问题？是否需要在编译过程中定义？有工作吗？

非常感谢

立即开始使用MVCE ..很快就会更新

函数模板问题

0 个答案: