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• raj_r Member - All Emails Posts: 987

  July 2019 edited July 2019

  @pgv i think there is a mail from me that is stuck in some queue
  @santosh_kumar std::vector->size() is a function i dont think watch windows can evaluate function results
  it can only typecast a memory location
  you can do dx systemHandles.size() using the new natvis expression evaluator it will provide you the vector size

  0:000> dv  
  g1 = { size=5 } 
  0:000> ?? g1 
  class std::vector<int,std::allocator > 
  +0x000 _Mypair : std::_Compressed_pair<std::allocator,std::_Vector_val<std::_Simple_types >,1> 
  0:000> dx g1.size() <<<<<<<<<<<<<<<<< 
  g1.size() : 5 <<<<<<<<<<<<<<<<<<< 

  0:000> dx -r 9 g1 
  g1 : { size=5 } [Type: std::vector<int,std::allocator >] 
  [] [Type: std::vector<int,std::allocator >] 
  [capacity] : 6 
  [allocator] : allocator [Type: std::_Compressed_pair<std::allocator,std::_Vector_val<std::_Simple_types >,1>] 
  [] [Type: std::_Compressed_pair<std::allocator,std::_Vector_val<std::_Simple_types >,1>] 
  [0] : 1 [Type: int] 
  [1] : 2 [Type: int] 
  [2] : 3 [Type: int] 
  [3] : 4 [Type: int] 
  [4] : 5 [Type: int] 

  check this stack overflow post

  Post edited by raj_r on July 2019

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• raj_r Member - All Emails Posts: 987

  July 2019 edited July 2019

  the other day i was mucking around with some vectors in windbg and i happened
  to unassemble the vector::size() function
  looking at the disassembly and the crt src for the same function
  i happened to realize that you can set a transparent expression in the watch window to look at the vector::size()

  here is the disassembly of size() function for a vector in question

  :000> x vect!std::vector<int,std::allocator<int> >::size
  00007ff7`57cfa6f0 vect!std::vector<int,std::allocator<int> >::size (void)
  0:000> uf 7ff757cfa6f0
  vect!std::vector<int,std::allocator<int> >::size 
   [c:\program files (x86)\microsoft visual studio\2017\community\vc\tools\msvc\14.16.27023\include\vector @ 1703]:
   1703 00007ff7`57cfa6f0 48894c2408      mov     qword ptr [rsp+8],rcx
   1703 00007ff7`57cfa6f5 4883ec38        sub     rsp,38h
   1704 00007ff7`57cfa6f9 488b4c2440      mov     rcx,qword ptr [rsp+40h]
   1704 00007ff7`57cfa6fe e8bca9feff      call    vect!ILT+16570
   1704 00007ff7`57cfa703 4889442420      mov     qword ptr [rsp+20h],rax
   1704 00007ff7`57cfa708 488b4c2440      mov     rcx,qword ptr [rsp+40h]
   1704 00007ff7`57cfa70d e85a93feff      call    vect!ILT+10855
   1704 00007ff7`57cfa712 488b00          mov     rax,qword ptr [rax]
   1704 00007ff7`57cfa715 488b4c2420      mov     rcx,qword ptr [rsp+20h]
   1704 00007ff7`57cfa71a 488b09          mov     rcx,qword ptr [rcx]
   1704 00007ff7`57cfa71d 482bc8          sub     rcx,rax
   1704 00007ff7`57cfa720 488bc1          mov     rax,rcx
   1704 00007ff7`57cfa723 48c1f802        sar     rax,2
   1705 00007ff7`57cfa727 4883c438        add     rsp,38h
   1705 00007ff7`57cfa72b c3              ret
  windbg> .open -a 7ff757cfa6f0
  

  and the relevent src code from crt sources

              _NODISCARD size_type size() const noexcept
                  {   // return length of sequence
                  return (static_cast<size_type>(this->_Mylast() - this->_Myfirst()));
                  }
  

  so basically if you set a watch expression like

  systemHandles._Mypair._Myval2._Mylast - systemHandles._Mypair._Myval2._Myfirst

  windbg will resolve the size() in the watch window (it will do the pointer arithmetic and display the actual size if you are wondering

  how address x - address y each being 8 bytes wide result in 5

  0:000> ?? g1._Mypair._Myval2._Mylast
  int * 0x0000026f`5e0197a4
  0:000> ?? g1._Mypair._Myval2._Mylast - g1._Mypair._Myval2._Myfirst
  int64 0n5
  0:000> ?? 0x0000026f`5e0197a4 - 0x0000026f`5e019790
  int64 0n20
  0:000> ?? ( 0x0000026f`5e0197a4 - 0x0000026f`5e019790 ) / sizeof(int)
  unsigned int64 5
  

  

  Post edited by raj_r on July 2019

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