// Consider the program below. I have a question about it's behavior.
#include <sigc++/sigc++.h>
#include <iostream>
#include <string>
using namespace std;
class Physical : public sigc::trackable
{
public:
Physical(int i) : id(i) {}
virtual ~Physical() {}
bool present(int i, Physical* phy)
{
if (id == i)
{
phy = this;
cout << "Physical::present(): this: "
<< this << ", phy: " << phy << endl;
phy->print("We put 'this' address in 'phy'."); // same as print().
cout << "phy->id: " << phy->id << endl; // same as id.
return true;
}
return false;
}
void print(const string& msg)
{ cout << msg << endl; }
private:
int id;
};
int main()
{
sigc::signal< bool, int, Physical* > signal_present;
int id = 9;
Physical p1(3), p2(id), p3(17), p4(22);
Physical* phy = 0;
bool answer = false;
answer = signal_present.emit(4, phy); // Shows that not an instance,
// does not affect us.
cout << "answer: " << answer << ", phy: " << phy << endl;
signal_present.connect(sigc::mem_fun(p1, &Physical::present));
signal_present.connect(sigc::mem_fun(p2, &Physical::present));
signal_present.connect(sigc::mem_fun(p3, &Physical::present));
signal_present.connect(sigc::mem_fun(p4, &Physical::present));
answer = signal_present.emit(7, phy); // Asking for an object of non existent
// id, gives no response, as desired.
answer = signal_present.emit(id, phy);// But this id exists.
cout << "answer: " << answer << ", phy: " << phy << endl;
if (answer)
{ cout << "An instance of id " << id << " is present.\n"; }
if (phy)
{ phy->print("It works as assumed.\n"); }
}
/*
* compilation:
* g++ sigc++_test.cc -o sigc++_test \
* `pkg-config sigc++-2.0 --cflags --libs`
*
* output:
* answer: 0, phy: 0
* Physical::present(): this: 0xbffff820, phy: 0xbffff820
* We put 'this' address in 'phy'.
* phy->id: 9
* answer: 0, phy: 0
*
* question:
* Why phy is 0 after signal emission? It was not null
* inside Physical::present(). Also answer is 0. What am I missing?
* What is the alternative to get address of phy similar to this method?
* I will be pleased for a detailed answer.
*/
// -- Kashif Masood
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