将函数作为参数传入 C++ 时出错

Question

I have a working implementation of testing the time of a function for search methods, which take:

checkSearchTime(T(*funcPointer) (T myArray[], int size, T wanted)

as parameters, I try to do the same thing with sort methods:

checkSortTime(T(*funcPointer) (T myArray[],int size)

and I get an error. This is the error:

Error   C2664   'void checkSortTime<int>(T (__cdecl *)(T [],int),T [],int)': cannot convert argument 1 from 'void (__cdecl *)(T [],int)' to 'T (__cdecl *)(T [],int)'   

Here is the code for both files:

int main() {
    memLeaks();
    constexpr auto SIZE = 5;
    int myArray[SIZE];
    populateArrayRandom(myArray, SIZE);
    PrintArray(myArray, SIZE);
    //insertionSort(myArray, SIZE);
    PrintArray(myArray, SIZE);
    
    checkSearchTime(binary_search, myArray, SIZE, 12);
    checkSortTime(selectionSort, myArray, SIZE); // THIS IS WHERE THE ERROR IS

    //checkAllSorts(myArray, SIZE); // WOULD LIKE TO CALL THIS AFTER
}


template<typename T>   
void checkSearchTime(T(*funcPointer) (T myArray[], int size, T wanted),
    T arrayArgument[], int sizeArgument, T wantedArgument) {
    
    // Use auto keyword to avoid typing long
    auto start = std::chrono::high_resolution_clock::now();
    funcPointer(arrayArgument, sizeArgument, wantedArgument);
    auto stop = std::chrono::high_resolution_clock::now();
    auto duration = std::chrono::duration_cast<std::chrono::nanoseconds>(stop - start);

    //std::cout << "Microseconds: " << duration.count() << std::endl;
    std::cout << "[" << duration.count() << "] Nanoseconds" << std::endl;
}

template<typename T>                                                             
void checkAllSearches(T myArray[], int size, T value) {
    std::cout << "Search Implementations and Timing\n";
    std::cout << "Binary=";
    checkSearchTime(binary_search, myArray, size, value);
    std::cout << "Linear=";
    checkSearchTime(linear_search, myArray, size, value);
    std::cout << "JumpSearch=";
    checkSearchTime(jump_search, myArray, size, value);
    std::cout << "Exponential=";
    checkSearchTime(exponential_search, myArray, size, value);
    std::cout << "FibMonaccian=";
    checkSearchTime(fibMonaccian_search, myArray, size, value);
}

template<typename T>                                                                                
void checkSortTime(T(*funcPointer) (T myArray[],int size), //tried const here, doesn't work either
    T arrayArgument[], int sizeArgument) {
    // Use auto keyword to avoid typing long
    auto start = std::chrono::high_resolution_clock::now();
    funcPointer(arrayArgument, sizeArgument);
    auto stop = std::chrono::high_resolution_clock::now();
    auto duration = std::chrono::duration_cast<std::chrono::nanoseconds>(stop - start);

    //std::cout << "Microseconds: " << duration.count() << std::endl;
    std::cout << "[" << duration.count() << "] Nanoseconds" << std::endl;
}

Answer 1

Nvm 这是因为排序方法不返回任何东西 =)

Answer 2

As you have already figured it out, the return type of your sort function ( selectionSort ) must have been void .

So, I am just posting this answer for others that might face a similar issue.

Changing this

template<typename T>                                                                                
void checkSortTime(T(*funcPointer)

to the following, will solve the issue:

void checkSortTime(void(*funcPointer)

Answer 3

Not really an answer, but just to let you know: passing arrays by "const T(&name)[const size]" keeps the size with the array. And you promise not to change its content (const). This syntax can also be used in templates like this (In this example I just return the value, didn't update to return void):

#include <iostream>

template<typename T, std::size_t N>
T checkSearchTime(T(*funcPointer)(const T(&myArray)[N], const T& wanted), const T (&arrayArgument)[N], const T& wantedArgument)
{
    return funcPointer(arrayArgument, wantedArgument);
}

template<std::size_t N>
int lookup(const int(&arr)[N], const int& value)
{
    for (int i = 0; i < N; ++i) std::cout << i << " ";
    std::cout << "\n";
    return value;
}

int main()
{
    int arr[]{ 1,2,3,4,5 };
    int wanted = 3;
    int value = checkSearchTime(lookup, arr, wanted);
    std::cout << "value = " << value;
}

Happy coding