Error while accessing map of int to class objects in c++ - c++

Question

I have this map map<int, PageTableEntry>> processmapram where the key is an integer and the value is the class object. This is how values are inserted to it.
for(i=0;i<lenDataSegment;i+=PG_SIZE)
{
int ramloc = getFreeSpaceRAM();
if(ramloc == -1)
{
int swaploc = getFreeSwapSpace();
bitmapSWAP[swaploc/PG_SIZE] = 1;
PageTableEntry pte(swaploc, 1, 0);
processmapram.insert({i, pte}); \\ insert values to map
strncpy(pSWap+swaploc, DataSeg+i, PG_SIZE);
}
else
{
bitmapRAM[ramloc/PG_SIZE] = 1;
PageTableEntry pte(ramloc, 0, 1);
processmapram.insert({i, pte}); \\ insert values to map
strncpy(pRAM+ramloc, DataSeg+i, PG_SIZE);
}
}
The PageTableEntry structure is defined as
typedef struct PageTableEntry {
int phyadd;
int flagswap;
int flagram;
PageTableEntry(int phyadd, int flagswap, int flagram)
{
this->phyadd = phyadd;
this->flagswap = flagswap;
this->flagram = flagram;
}
} PageTableEntry;
Now when I am accessing the same in another function I am getting an error :
int Process::readAddress(int virtualAddr, int lenToRead, char *buf)
{
cout<<processmapram[virtualAddr].phyadd;
}
or like this
PageTableEntry pte(-1,0,0);
pte = mymap[virtualAddr];
cout<<pte.phyadd;
Error :
In file included from /usr/include/c++/7/functional:54:0,
from /usr/include/x86_64-linux-gnu/c++/7/bits/stdc++.h:71,
from Process.h:1,
from ProcessManager.h:1,
from Process.cpp:3:
/usr/include/c++/7/tuple: In instantiation of ‘std::pair<_T1, _T2>::pair(std::tuple<_Args1 ...>&, std::tuple<_Args2 ...>&, std::_Index_tuple<_Indexes1 ...>, std::_Index_tuple<_Indexes2 ...>) [with _Args1 = {const int&}; long unsigned int ..._Indexes1 = {0}; _Args2 = {}; long unsigned int ..._Indexes2 = {}; _T1 = const int; _T2 = PageTableEntry]’:
/usr/include/c++/7/tuple:1641:63: required from ‘std::pair<_T1, _T2>::pair(std::piecewise_construct_t, std::tuple<_Args1 ...>, std::tuple<_Args2 ...>) [with _Args1 = {const int&}; _Args2 = {}; _T1 = const int; _T2 = PageTableEntry]’
/usr/include/c++/7/ext/new_allocator.h:136:4: required from ‘void __gnu_cxx::new_allocator<_Tp>::construct(_Up*, _Args&& ...) [with _Up = std::pair<const int, PageTableEntry>; _Args = {const std::piecewise_construct_t&, std::tuple<const int&>, std::tuple<>}; _Tp = std::_Rb_tree_node<std::pair<const int, PageTableEntry> >]’
/usr/include/c++/7/bits/alloc_traits.h:475:4: required from ‘static void std::allocator_traits<std::allocator<_CharT> >::construct(std::allocator_traits<std::allocator<_CharT> >::allocator_type&, _Up*, _Args&& ...) [with _Up = std::pair<const int, PageTableEntry>; _Args = {const std::piecewise_construct_t&, std::tuple<const int&>, std::tuple<>}; _Tp = std::_Rb_tree_node<std::pair<const int, PageTableEntry> >; std::allocator_traits<std::allocator<_CharT> >::allocator_type = std::allocator<std::_Rb_tree_node<std::pair<const int, PageTableEntry> > >]’
/usr/include/c++/7/bits/stl_tree.h:626:32: required from ‘void std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_construct_node(std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_Link_type, _Args&& ...) [with _Args = {const std::piecewise_construct_t&, std::tuple<const int&>, std::tuple<>}; _Key = int; _Val = std::pair<const int, PageTableEntry>; _KeyOfValue = std::_Select1st<std::pair<const int, PageTableEntry> >; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, PageTableEntry> >; std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_Link_type = std::_Rb_tree_node<std::pair<const int, PageTableEntry> >*]’
/usr/include/c++/7/bits/stl_tree.h:643:21: required from ‘std::_Rb_tree_node<_Val>* std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_create_node(_Args&& ...) [with _Args = {const std::piecewise_construct_t&, std::tuple<const int&>, std::tuple<>}; _Key = int; _Val = std::pair<const int, PageTableEntry>; _KeyOfValue = std::_Select1st<std::pair<const int, PageTableEntry> >; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, PageTableEntry> >; std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_Link_type = std::_Rb_tree_node<std::pair<const int, PageTableEntry> >*]’
/usr/include/c++/7/bits/stl_tree.h:2398:33: required from ‘std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::iterator std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_emplace_hint_unique(std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::const_iterator, _Args&& ...) [with _Args = {const std::piecewise_construct_t&, std::tuple<const int&>, std::tuple<>}; _Key = int; _Val = std::pair<const int, PageTableEntry>; _KeyOfValue = std::_Select1st<std::pair<const int, PageTableEntry> >; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, PageTableEntry> >; std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::iterator = std::_Rb_tree_iterator<std::pair<const int, PageTableEntry> >; std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::const_iterator = std::_Rb_tree_const_iterator<std::pair<const int, PageTableEntry> >]’
/usr/include/c++/7/bits/stl_map.h:493:8: required from ‘std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const key_type&) [with _Key = int; _Tp = PageTableEntry; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, PageTableEntry> >; std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type = PageTableEntry; std::map<_Key, _Tp, _Compare, _Alloc>::key_type = int]’
Process.cpp:19:26: required from here
/usr/include/c++/7/tuple:1652:70: error: no matching function for call to ‘PageTableEntry::PageTableEntry()’
second(std::forward<_Args2>(std::get<_Indexes2>(__tuple2))...)
^
In file included from ProcessManager.h:1:0,
from Process.cpp:3:
Process.h:80:2: note: candidate: PageTableEntry::PageTableEntry(int, int, int)
PageTableEntry(int phyadd, int flagswap, int flagram)
^~~~~~~~~~~~~~
Process.h:80:2: note: candidate expects 3 arguments, 0 provided
Process.h:76:16: note: candidate: constexpr PageTableEntry::PageTableEntry(const PageTableEntry&)
typedef struct PageTableEntry {
^~~~~~~~~~~~~~
Process.h:76:16: note: candidate expects 1 argument, 0 provided
Process.h:76:16: note: candidate: constexpr PageTableEntry::PageTableEntry(PageTableEntry&&)
Process.h:76:16: note: candidate expects 1 argument, 0 provided
Note : The example posted here is the minimal code for a large project. I have just posted minimal reproducible example here.

Answer 1

I think in your Process::readAddress function you want to print an existing entry.
So you need to make sure that required entry is found in the map, rather than silently creating a new one for each virtualAddr - that is what operator[] will do and for what it needs default ctor, as others mentioned in the comments. You can use std::map::find
int Process::readAddress(int virtualAddr, int lenToRead, char *buf)
{
auto it = processmapram.find(virtualAddr);
if(it != processmapram.end())
{
cout << it->second.phyadd;
}
}