Error in vector of struct with implemented Functions - c++

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
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.
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;
};
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