Howto use non-static member function for template argument? - c++

Question

I have this minimal sample code:
#include <functional>
#include <iostream>
#include <vector>
template<class ReadFileCallback>
void fileMgr_ReadWithCallback(std::string filename, ReadFileCallback callback) {
callback("OK");
}
void globalReadResult(std::string result) {
std::cout << "ReadResult in global function: result=" << result << std::endl;
}
class MyClass {
public:
MyClass() {};
~MyClass() {};
void Read() {
fileMgr_ReadWithCallback("file", globalReadResult);
//fileMgr_ReadWithCallback("file", this->ReadResult);
}
void ReadResult(std::string result) {
std::cout << "ReadResult in member function: result=" << result << std::endl;
}
};
int main()
{
MyClass c;
c.Read();
return 0;
}
For callback function I'd like to use a non-static class member MyClass::ReadResult. It would also be good to know before calling the callback if the object is still valid (non-destructed), because otherwise the program will fail I guess.
How shall I change this code to be able to use the MyClass object's ReadResult as callback?

Answer 1

You can just wrap it into a lambda:
class MyClass {
public:
MyClass() {};
~MyClass() {};
void Read() {
fileMgr_ReadWithCallback("file", [this](const std::string& result){ this->ReadResult(result); });
}
void ReadResult(std::string result) {
std::cout << "ReadResult in member function: result=" << result << std::endl;
}
};

Answer 2

You may use std::bind.
#include <functional>
#include <iostream>
#include <vector>
#include <functional>
template<class ReadFileCallback>
void fileMgr_ReadWithCallback(std::string filename, ReadFileCallback callback) {
callback("OK");
}
void globalReadResult(std::string result) {
std::cout << "ReadResult in global function: result=" << result << std::endl;
}
class MyClass {
public:
MyClass() {};
~MyClass() {};
void Read() {
using std::placeholders::_1;
//std::function<void(std::string)> func = std::bind( &MyClass::ReadResult, this, _1);
auto func = std::bind( &MyClass::ReadResult, this, _1);
fileMgr_ReadWithCallback("file", func);
//
// or
// fileMgr_ReadWithCallback("file", std::bind( &MyClass::ReadResult, this, _1));
}
void ReadResult(std::string result) {
std::cout << "ReadResult in member function: result=" << result << std::endl;
}
};
int main()
{
MyClass c;
c.Read();
return 0;
}