Error in vector of struct with implemented Functions

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