c++ - Error C2678: binary '<<' : no operator found which takes a left-hand operand of type 'const std::ofstream' (or there is no acceptable conversion) -

i working on mfc application , have declared ofstream object in class header, object initialized in constructor , used in other methods of same class. got following error:

error c2678: binary '<<' : no operator found takes left-hand operand of type 'const std::ofstream' (or there no acceptable conversion)

i have searched issue , found many solutions i.e. there suggestions to:

• use #include <string>
• use #include <iostream>
• use #include <istream>

and other information got when error occur. got doesn't fix issue. kindly have @ code:

cgroupcombobox.h :

private:     std::ofstream fptr; 

cgroupcombobox.cpp :

//constructor cgroupcombobox::cgroupcombobox()     : m_dropdownlistautowidth(true)     , m_autocomplete(true)     , m_selectionundobyesckey(true) {     fptr.open("test.txt",std::ios::out); //initialization of fptr }  //member function int cgroupcombobox::findstring(int nstartafter, lpctstr lpszstring) const {     fptr<<"i findstring.\n"; //trying write      //other code }  //destructor cgroupcombobox::~cgroupcombobox() {     //other code      fptr.close(); } 

what doing wrong here?

you declared member function qualifier const

int cgroupcombobox::findstring(int nstartafter, lpctstr lpszstring) const                                                                     ^^^^^ 

thus this in case has type const cgroupcombobox * , may not change data member of object pointed this.

however statements

fptr<<"i findstring.\n"; //trying write 

requires non-const data member fptr.

so compiler issues error.

one of solutions use specifier mutable data member fptr