Functions with a map as parameter not working - c++

Question

For some reason, all of the functions in my program with a map as a parameter are not working. This function is the one that calls all of them (pageAndTimestamp is a struct btw):
void fifo(int framesize, int numref, int* pagestream)
{
double hit = 0, size = numref;
map<int, pageAndTimestamp> frames = frameMaker(framesize);
for (int time = 0; time < numref; time++)
{
if (pageLoaded(pagestream[time], frames))
{
hit++;
output(time, pagestream[time], size, hit, frames);
}
else
{
int loc = findPageToReplace(frames);
replacePage(loc, pagestream[time], time, frames);
output(time, pagestream[time], size, hit, frames);
}
}
}
These are the functions that are not working properly:
bool pageLoaded(int page, map<int, pageAndTimestamp> m)
{
for (const auto& it : m)
{
if (it.second.a[0] == page)
return true;
}
return false;
}
int findPageToReplace(map<int, pageAndTimestamp> m)
{
int timestamp = INT_MAX;
int replaceLoc = 0;
for (const auto& it : m)
{
if (it.second.a[1] == -1)
return it.first;
else
{
if (it.second.a[1] < timestamp)
{
timestamp = it.second.a[1];
replaceLoc = it.first;
}
}
}
return replaceLoc;
}
void replacePage(int loc, int page, int time, map<int, pageAndTimestamp> m)
{
m.at(loc).a[0] = page;
m.at(loc).a[1] = time;
}
void output(int t, int p, double s, double h, map<int, pageAndTimestamp> m)
{
cout << "Time: " << t << endl << "Page: " << p << endl;
for(const auto& it : m)
cout << "Frame" << it.first << ": " << it.second.a[0] << endl;
cout << "Hit ratio: " << h << " / " << s << " (" << h / s << ")" << endl
<< endl << endl;
}
When I run the program in the Visual Studio 2017 debugger, when I step into any of the above functions, the debugger takes me to this function header in the map standard header:
map(const map& _Right)
: _Mybase(_Right, _Alnode_traits::select_on_container_copy_construction(_Right._Getal()))
{ // construct map by copying _Right
}
I don't know what the problem is, or why the debugger is taking me to this function header. How do I fix this?

Answer 1

The function replacePage for example, is defined as:
void replacePage(int loc, int page, int time, map<int, pageAndTimestamp> m)
This function takes a map as a value, not a reference or pointer. Thus, when you call it as follows:
replacePage(loc, pagestream[time], time, frames);
then the map frames is copied into the variable m in your function. This is why the debugger, for example, takes you to the copy constructor for a map.
Further, it means that the replacePage code
m.at(loc).a[0] = page;
m.at(loc).a[1] = time;
is making its changes to a copy of frames, not frames itself.
You probably want functions with signatures of the form:
bool pageLoaded(int page, const map<int, pageAndTimestamp>& m)
int findPageToReplace(const map<int, pageAndTimestamp>& m)
void replacePage(int loc, int page, int time, map<int, pageAndTimestamp>& m)
void output(int t, int p, double s, double h, const map<int, pageAndTimestamp>& m)
in which most of the functions take a constant reference, while replacePage requires a (non-const) reference.