具有已实现函数的结构向量中的错误

Question

I get the Erro:

"no instance of constructor "std::vector<_Ty, _Alloc>::vector 
 [with _Ty=FunctionToUpdate, _Alloc=std::allocator<FunctionToUpdate>]" matches the argument list" 

No matter how I change it, it persists, as long I keep it as a class. If I keep it all in just a simple .cpp without class and header, it all resolves easily. My.h:

#include <vector>
#include <functional>
#include <iostream>

struct Params
{
    std::vector<int> Integers;
    std::vector<std::string> Strings;
};

struct FunctionToUpdate
{
    int Version;
    std::function<void(int, Params)> Function;
    Params Parameters;
};

class Error
{
public:
    Error();
    void testFunctionA(int a, Params p);
    void testFunctionB(int a, Params p);
protected:
    const static std::vector<FunctionToUpdate> table;
};

Here is my .cpp , please assist me, I can't find the error:

#include "ErrorHandling.h"

Error::Error()
{
    for (auto functionToUpdate : table)
    {
        functionToUpdate.Function(functionToUpdate.Version, functionToUpdate.Parameters);
        std::cout << "############################################" << std::endl;
    }
    std::cout << "Done!" << std::endl;
}

void Error::testFunctionA(int a, Params parameter)
{
    //std::cout << "Size Integers: " << parameter.Integers.size() << std::endl;
    //std::cout << "Size Strings: " << parameter.Strings.size() << std::endl;

    std::cout << a << std::endl;

    for (auto& integer : parameter.Integers)
    {
        std::cout << integer << std::endl;
    }
    for (auto& integer : parameter.Strings)
    {
        std::cout << integer << std::endl;
    }
}

void Error::testFunctionB(int a, Params parameter)
{
    std::cout << a << std::endl;
    std::cout << parameter.Integers.at(0) << std::endl;
}

const std::vector<FunctionToUpdate> Error::table
{                                                       // <-- here the Error happens
    { 100, &testFunctionA, { {177}}},
    { 1948, &testFunctionB, { {314}}},
};

int main()
{
    Error error;
}

Answer 1

Your code has a few issues

1. First, the correct initialization of static member Error::table would be as follows:

    const std::vector<FunctionToUpdate> Error::table { { 100, &Error::testFunctionA, { { {177} }, { {"string"} } }}, { 1948, &Error::testFunctionB, { { {314} }, { {"string"} } } } };

   Note that the syntax &Error::testFunctionA for addressing the member function pointer. Additionally, the Params has two vectors. One is std::vector<int> and the other is std::vector<std::string> . In your code, the std::vector<std::string> has not been mentioned.

2. In FunctionToUpdate the member function pointer type is wrong. Using typed member function pointer , you could

   // forward declaration class Error; // member function pointer type using ErrorFunType = void(Error::*)(int, Params); struct FunctionToUpdate { int Version; ErrorFunType Function; Params Parameters; };

3. Secondly, the call to pointer to the member function in Error::Error() is wrong. It needs an ( Error class) instance to call with . For example:

    for (auto functionToUpdate : table) { (this->*functionToUpdate.Function)( functionToUpdate.Version, functionToUpdate.Parameters ); // or more generic `std::invoke` (since c++17) // std::invoke(functionToUpdate.Function // , this, functionToUpdate.Version // , functionToUpdate.Parameters); // ... }

The above changes will make, your code compiles again !

---

In case of wondering, how to handle the pointer to member function with std::function , (one way) to wrap the instance to call the member along with the std::function type.

Following is the example:

// forward declaration
class Error;
// member function pointer
using ErrorFunType = std::function<void(Error*, int, Params)>;

struct FunctionToUpdate
{
    int Version;
    ErrorFunType Function;
    Params Parameters;
};

now in Error::Error()

Error::Error()
{
    for (auto functionToUpdate : table)
    {
        functionToUpdate.Function(this
            , functionToUpdate.Version, functionToUpdate.Parameters);
    }
}

See a demo