c++ - Using overloaded operator+ without assingment -
i have simple(not simple) question: possibility overloaded operator+ working not want when won't use assingment overloaded operator?
example:
object a, b, c; //here code add numbers object , b; c=a+b; cout << c; and thing is: when i'm using overloaded assingment operator, fine. without this, elements in c gets random numbers. why?
and question: why can't overloaded << , + operators:
cout << a+b; edit: here code:
#include <iostream> #include <cstdio> using namespace std; class list; class element{ private: int number; element* next; friend class list; friend ostream & operator<<(ostream &, list &); public: element(int data){ number=data; } int getdata(){ return number; } }; class list{ private: element* head; int size; friend ostream & operator<<(ostream &, list &); public: list(){ head=null; size=0; } list(const list &lista){ //cout << "wyw" << endl; //fflush(stdout); if (lista.size==0){ size=0; head=null; } else { size=0; head=null; element* tmp=lista.head; while(tmp!=null){ cout << tmp->number << " "; fflush(stdout); this->addtolist(tmp->number); tmp=tmp->next; } } } ~list(){ if (head!=null){ element* tmp=head; element *temp; while(tmp!=null){ temp=tmp->next; delete tmp; tmp=temp; } head=null; } } void addtolist(int data){ element* newnode=new element(data); newnode->next=null; element *tmp=head; if (tmp!=null){ while(tmp->next!=null){ tmp=tmp->next; } tmp->next=newnode; } else{ head=newnode; } size++; } list& operator=(const list& lista){ if (&lista==this) return *this; if (this->head!=null){ element* tmp=head; element *temp; while(tmp!=null){ temp=tmp->next; delete tmp; tmp=temp; } head=null; } if (lista.size==0){ size=0; head=null; } else { size=0; head=null; element* tmp=lista.head; while(tmp!=null){ this->addtolist(tmp->number); tmp=tmp->next; } } return *this; } list operator+(const list &lista){ list newlist; element *tmp=this->head; while (tmp!=null){ newlist.addtolist(tmp->number); tmp=tmp->next; } tmp=lista.head; while (tmp!=null){ newlist.addtolist(tmp->number); tmp=tmp->next; } return newlist; } }; istream & operator>>(istream &str, list &lists){ int data; str >> data; lists.addtolist(data); return str; } ostream & operator<<(ostream &str, list &lists){ element*tmp=lists.head; if (tmp==null){ str << "list empty" << endl; } else{ while(tmp!=null){ str << tmp->number << "--"; tmp=tmp->next; } str << "null" << endl << "size of lsit: " << lists.size << endl; } return str; } int main(){ list lista; cin >> lista; cin >> lista; list list2=lista; cout << lista; cout << list2; list c; //cout << list2+lista; cant that, why? c=list2+lista; cout << c; return 0; } @drewdormann here error:
lista.cpp: in function ‘int main()’: lista.cpp:167:7: error: no match ‘operator<<’ (operand types ‘std::ostream {aka std::basic_ostream<char>}’ , ‘list’) cout << lista+list2; ^ lista.cpp:167:7: note: candidates are: in file included /usr/include/c++/4.8/iostream:39:0, lista.cpp:1: /usr/include/c++/4.8/ostream:108:7: note: std::basic_ostream<_chart, _traits>::__ostream_type& std::basic_ostream<_chart, _traits>::operator<<(std::basic_ostream<_chart, _traits>::__ostream_type& (*)(std::basic_ostream<_chart, _traits>::__ostream_type&)) [with _chart = char; _traits = std::char_traits<char>; std::basic_ostream<_chart, _traits>::__ostream_type = std::basic_ostream<char>] operator<<(__ostream_type& (*__pf)(__ostream_type&)) ^ /usr/include/c++/4.8/ostream:108:7: note: no known conversion argument 1 ‘list’ ‘std::basic_ostream<char>::__ostream_type& (*)(std::basic_ostream<char>::__ostream_type&) {aka std::basic_ostream<char>& (*)(std::basic_ostream<char>&)}’ /usr/include/c++/4.8/ostream:117:7: note: std::basic_ostream<_chart, _traits>::__ostream_type& std::basic_ostream<_chart, _traits>::operator<<(std::basic_ostream<_chart, _traits>::__ios_type& (*)(std::basic_ostream<_chart, _traits>::__ios_type&)) [with _chart = char; _traits = std::char_traits<char>; std::basic_ostream<_chart, _traits>::__ostream_type = std::basic_ostream<char>; std::basic_ostream<_chart, _traits>::__ios_type = std::basic_ios<char>] operator<<(__ios_type& (*__pf)(__ios_type&)) ^ /usr/include/c++/4.8/ostream:117:7: note: no known conversion argument 1 ‘list’ ‘std::basic_ostream<char>::__ios_type& (*)(std::basic_ostream<char>::__ios_type&) {aka std::basic_ios<char>& (*)(std::basic_ios<char>&)}’ /usr/include/c++/4.8/ostream:127:7: note: std::basic_ostream<_chart, _traits>::__ostream_type& std::basic_ostream<_chart, _traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _chart = char; _traits = std::char_traits<char>; std::basic_ostream<_chart, _traits>::__ostream_type = std::basic_ostream<char>] operator<<(ios_base& (*__pf) (ios_base&)) ^ /usr/include/c++/4.8/ostream:127:7: note: no known conversion argument 1 ‘list’ ‘std::ios_base& (*)(std::ios_base&)’ /usr/include/c++/4.8/ostream:166:7: note: std::basic_ostream<_chart, _traits>::__ostream_type& std::basic_ostream<_chart, _traits>::operator<<(long int) [with _chart = char; _traits = std::char_traits<char>; std::basic_ostream<_chart, _traits>::__ostream_type = std::basic_ostream<char>] operator<<(long __n) ^ /usr/include/c++/4.8/ostream:166:7: note: no known conversion argument 1 ‘list’ ‘long int’ /usr/include/c++/4.8/ostream:170:7: note: std::basic_ostream<_chart, _traits>::__ostream_type& std::basic_ostream<_chart, _traits>::operator<<(long unsigned int) [with _chart = char; _traits = std::char_traits<char>; std::basic_ostream<_chart, _traits>::__ostream_type = std::basic_ostream<char>] operator<<(unsigned long __n) ^ /usr/include/c++/4.8/ostream:170:7: note: no known conversion argument 1 ‘list’ ‘long unsigned int’ /usr/include/c++/4.8/ostream:174:7: note: std::basic_ostream<_chart, _traits>::__ostream_type& std::basic_ostream<_chart, _traits>::operator<<(bool) [with _chart = char; _traits = std::char_traits<char>; std::basic_ostream<_chart, _traits>::__ostream_type = std::basic_ostream<char>] operator<<(bool __n) ^ /usr/include/c++/4.8/ostream:174:7: note: no known conversion argument 1 ‘list’ ‘bool’ in file included /usr/include/c++/4.8/ostream:609:0, /usr/include/c++/4.8/iostream:39, lista.cpp:1: /usr/include/c++/4.8/bits/ostream.tcc:91:5: note: std::basic_ostream<_chart, _traits>& std::basic_ostream<_chart, _traits>::operator<<(short int) [with _chart = char; _traits = std::char_traits<char>] basic_ostream<_chart, _traits>:: ^ /usr/include/c++/4.8/bits/ostream.tcc:91:5: note: no known conversion argument 1 ‘list’ ‘short int’ in file included /usr/include/c++/4.8/iostream:39:0, lista.cpp:1: /usr/include/c++/4.8/ostream:181:7: note: std::basic_ostream<_chart, _traits>::__ostream_type& std::basic_ostream<_chart, _traits>::operator<<(short unsigned int) [with _chart = char; _traits = std::char_traits<char>; std::basic_ostream<_chart, _traits>::__ostream_type = std::basic_ostream<char>] operator<<(unsigned short __n) ^ /usr/include/c++/4.8/ostream:181:7: note: no known conversion argument 1 ‘list’ ‘short unsigned int’ in file included /usr/include/c++/4.8/ostream:609:0, /usr/include/c++/4.8/iostream:39, lista.cpp:1: /usr/include/c++/4.8/bits/ostream.tcc:105:5: note: std::basic_ostream<_chart, _traits>& std::basic_ostream<_chart, _traits>::operator<<(int) [with _chart = char; _traits = std::char_traits<char>] basic_ostream<_chart, _traits>:: ^ /usr/include/c++/4.8/bits/ostream.tcc:105:5: note: no known conversion argument 1 ‘list’ ‘int’ in file included /usr/include/c++/4.8/iostream:39:0, lista.cpp:1: /usr/include/c++/4.8/ostream:192:7: note: std::basic_ostream<_chart, _traits>::__ostream_type& std::basic_ostream<_chart, _traits>::operator<<(unsigned int) [with _chart = char; _traits = std::char_traits<char>; std::basic_ostream<_chart, _traits>::__ostream_type = std::basic_ostream<char>] operator<<(unsigned int __n) ^ /usr/include/c++/4.8/ostream:192:7: note: no known conversion argument 1 ‘list’ ‘unsigned int’ /usr/include/c++/4.8/ostream:201:7: note: std::basic_ostream<_chart, _traits>::__ostream_type& std::basic_ostream<_chart, _traits>::operator<<(long long int) [with _chart = char; _traits = std::char_traits<char>; std::basic_ostream<_chart, _traits>::__ostream_type = std::basic_ostream<char>] operator<<(long long __n) ^ /usr/include/c++/4.8/ostream:201:7: note: no known conversion argument 1 ‘list’ ‘long long int’ /usr/include/c++/4.8/ostream:205:7: note: std::basic_ostream<_chart, _traits>::__ostream_type& std::basic_ostream<_chart, _traits>::operator<<(long long unsigned int) [with _chart = char; _traits = std::char_traits<char>; std::basic_ostream<_chart, _traits>::__ostream_type = std::basic_ostream<char>] operator<<(unsigned long long __n) ^ /usr/include/c++/4.8/ostream:205:7: note: no known conversion argument 1 ‘list’ ‘long long unsigned int’ /usr/include/c++/4.8/ostream:220:7: note: std::basic_ostream<_chart, _traits>::__ostream_type& std::basic_ostream<_chart, _traits>::operator<<(double) [with _chart = char; _traits = std::char_traits<char>; std::basic_ostream<_chart, _traits>::__ostream_type = std::basic_ostream<char>] operator<<(double __f) ^ /usr/include/c++/4.8/ostream:220:7: note: no known conversion argument 1 ‘list’ ‘double’ /usr/include/c++/4.8/ostream:224:7: note: std::basic_ostream<_chart, _traits>::__ostream_type& std::basic_ostream<_chart, _traits>::operator<<(float) [with _chart = char; _traits = std::char_traits<char>; std::basic_ostream<_chart, _traits>::__ostream_type = std::basic_ostream<char>] operator<<(float __f) ^ /usr/include/c++/4.8/ostream:224:7: note: no known conversion argument 1 ‘list’ ‘float’ /usr/include/c++/4.8/ostream:232:7: note: std::basic_ostream<_chart, _traits>::__ostream_type& std::basic_ostream<_chart, _traits>::operator<<(long double) [with _chart = char; _traits = std::char_traits<char>; std::basic_ostream<_chart, _traits>::__ostream_type = std::basic_ostream<char>] operator<<(long double __f) ^ /usr/include/c++/4.8/ostream:232:7: note: no known conversion argument 1 ‘list’ ‘long double’ /usr/include/c++/4.8/ostream:245:7: note: std::basic_ostream<_chart, _traits>::__ostream_type& std::basic_ostream<_chart, _traits>::operator<<(const void*) [with _chart = char; _traits = std::char_traits<char>; std::basic_ostream<_chart, _traits>::__ostream_type = std::basic_ostream<char>] operator<<(const void* __p) ^ /usr/include/c++/4.8/ostream:245:7: note: no known conversion argument 1 ‘list’ ‘const void*’ in file included /usr/include/c++/4.8/ostream:609:0, /usr/include/c++/4.8/iostream:39, lista.cpp:1: /usr/include/c++/4.8/bits/ostream.tcc:119:5: note: std::basic_ostream<_chart, _traits>& std::basic_ostream<_chart, _traits>::operator<<(std::basic_ostream<_chart, _traits>::__streambuf_type*) [with _chart = char; _traits = std::char_traits<char>; std::basic_ostream<_chart, _traits>::__streambuf_type = std::basic_streambuf<char>] basic_ostream<_chart, _traits>:: ^ /usr/include/c++/4.8/bits/ostream.tcc:119:5: note: no known conversion argument 1 ‘list’ ‘std::basic_ostream<char>::__streambuf_type* {aka std::basic_streambuf<char>*}’ lista.cpp:141:12: note: std::ostream& operator<<(std::ostream&, list&) ostream & operator<<(ostream &str, list &lists){ ^ lista.cpp:141:12: note: no known conversion argument 2 ‘list’ ‘list&’ in file included /usr/include/c++/4.8/iostream:39:0, lista.cpp:1: /usr/include/c++/4.8/ostream:548:5: note: template<class _traits> std::basic_ostream<char, _traits>& std::operator<<(std::basic_ostream<char, _traits>&, const unsigned char*) operator<<(basic_ostream<char, _traits>& __out, const unsigned char* __s) ^ /usr/include/c++/4.8/ostream:548:5: note: template argument deduction/substitution failed: lista.cpp:167:16: note: cannot convert ‘list::operator+(const list&)((*(const list*)(& list2)))’ (type ‘list’) type ‘const unsigned char*’ cout << lista+list2; ^ in file included /usr/include/c++/4.8/iostream:39:0, lista.cpp:1: /usr/include/c++/4.8/ostream:543:5: note: template<class _traits> std::basic_ostream<char, _traits>& std::operator<<(std::basic_ostream<char, _traits>&, const signed char*) operator<<(basic_ostream<char, _traits>& __out, const signed char* __s) ^ /usr/include/c++/4.8/ostream:543:5: note: template argument deduction/substitution failed: lista.cpp:167:16: note: cannot convert ‘list::operator+(const list&)((*(const list*)(& list2)))’ (type ‘list’) type ‘const signed char*’ cout << lista+list2; ^ in file included /usr/include/c++/4.8/iostream:39:0, lista.cpp:1: /usr/include/c++/4.8/ostream:530:5: note: template<class _traits> std::basic_ostream<char, _traits>& std::operator<<(std::basic_ostream<char, _traits>&, const char*) operator<<(basic_ostream<char, _traits>& __out, const char* __s) ^ /usr/include/c++/4.8/ostream:530:5: note: template argument deduction/substitution failed: lista.cpp:167:16: note: cannot convert ‘list::operator+(const list&)((*(const list*)(& list2)))’ (type ‘list’) type ‘const char*’ cout << lista+list2; ^ in file included /usr/include/c++/4.8/ostream:609:0, /usr/include/c++/4.8/iostream:39, lista.cpp:1: /usr/include/c++/4.8/bits/ostream.tcc:321:5: note: template<class _chart, class _traits> std::basic_ostream<_chart, _traits>& std::operator<<(std::basic_ostream<_chart, _traits>&, const char*) operator<<(basic_ostream<_chart, _traits>& __out, const char* __s) ^ /usr/include/c++/4.8/bits/ostream.tcc:321:5: note: template argument deduction/substitution failed: lista.cpp:167:16: note: cannot convert ‘list::operator+(const list&)((*(const list*)(& list2)))’ (type ‘list’) type ‘const char*’ cout << lista+list2; ^ in file included /usr/include/c++/4.8/iostream:39:0, lista.cpp:1: /usr/include/c++/4.8/ostream:513:5: note: template<class _chart, class _traits> std::basic_ostream<_chart, _traits>& std::operator<<(std::basic_ostream<_chart, _traits>&, const _chart*) operator<<(basic_ostream<_chart, _traits>& __out, const _chart* __s) ^ /usr/include/c++/4.8/ostream:513:5: note: template argument deduction/substitution failed: lista.cpp:167:16: note: mismatched types ‘const _chart*’ , ‘list’ cout << lista+list2; ^ in file included /usr/include/c++/4.8/iostream:39:0, lista.cpp:1: /usr/include/c++/4.8/ostream:493:5: note: template<class _traits> std::basic_ostream<char, _traits>& std::operator<<(std::basic_ostream<char, _traits>&, unsigned char) operator<<(basic_ostream<char, _traits>& __out, unsigned char __c) ^ /usr/include/c++/4.8/ostream:493:5: note: template argument deduction/substitution failed: lista.cpp:167:16: note: cannot convert ‘list::operator+(const list&)((*(const list*)(& list2)))’ (type ‘list’) type ‘unsigned char’ cout << lista+list2; ^ in file included /usr/include/c++/4.8/iostream:39:0, lista.cpp:1: /usr/include/c++/4.8/ostream:488:5: note: template<class _traits> std::basic_ostream<char, _traits>& std::operator<<(std::basic_ostream<char, _traits>&, signed char) operator<<(basic_ostream<char, _traits>& __out, signed char __c) ^ /usr/include/c++/4.8/ostream:488:5: note: template argument deduction/substitution failed: lista.cpp:167:16: note: cannot convert ‘list::operator+(const list&)((*(const list*)(& list2)))’ (type ‘list’) type ‘signed char’ cout << lista+list2; ^ in file included /usr/include/c++/4.8/iostream:39:0, lista.cpp:1: /usr/include/c++/4.8/ostream:482:5: note: template<class _traits> std::basic_ostream<char, _traits>& std::operator<<(std::basic_ostream<char, _traits>&, char) operator<<(basic_ostream<char, _traits>& __out, char __c) ^ /usr/include/c++/4.8/ostream:482:5: note: template argument deduction/substitution failed: lista.cpp:167:16: note: cannot convert ‘list::operator+(const list&)((*(const list*)(& list2)))’ (type ‘list’) type ‘char’ cout << lista+list2; ^ in file included /usr/include/c++/4.8/iostream:39:0, lista.cpp:1: /usr/include/c++/4.8/ostream:476:5: note: template<class _chart, class _traits> std::basic_ostream<_chart, _traits>& std::operator<<(std::basic_ostream<_chart, _traits>&, char) operator<<(basic_ostream<_chart, _traits>& __out, char __c) ^ /usr/include/c++/4.8/ostream:476:5: note: template argument deduction/substitution failed: lista.cpp:167:16: note: cannot convert ‘list::operator+(const list&)((*(const list*)(& list2)))’ (type ‘list’) type ‘char’ cout << lista+list2; ^ in file included /usr/include/c++/4.8/iostream:39:0, lista.cpp:1: /usr/include/c++/4.8/ostream:471:5: note: template<class _chart, class _traits> std::basic_ostream<_chart, _traits>& std::operator<<(std::basic_ostream<_chart, _traits>&, _chart) operator<<(basic_ostream<_chart, _traits>& __out, _chart __c) ^ /usr/include/c++/4.8/ostream:471:5: note: template argument deduction/substitution failed: lista.cpp:167:16: note: deduced conflicting types parameter ‘_chart’ (‘char’ , ‘list’) cout << lista+list2; ^ in file included /usr/include/c++/4.8/string:52:0, /usr/include/c++/4.8/bits/locale_classes.h:40, /usr/include/c++/4.8/bits/ios_base.h:41, /usr/include/c++/4.8/ios:42, /usr/include/c++/4.8/ostream:38, /usr/include/c++/4.8/iostream:39, lista.cpp:1: /usr/include/c++/4.8/bits/basic_string.h:2753:5: note: template<class _chart, class _traits, class _alloc> std::basic_ostream<_chart, _traits>& std::operator<<(std::basic_ostream<_chart, _traits>&, const std::basic_string<_chart, _traits, _alloc>&) operator<<(basic_ostream<_chart, _traits>& __os, ^ /usr/include/c++/4.8/bits/basic_string.h:2753:5: note: template argument deduction/substitution failed: lista.cpp:167:16: note: ‘list’ not derived ‘const std::basic_string<_chart, _traits, _alloc>’ cout << lista+list2; i know when i'm trying use operaotr without overloading, here problem operator << overloaded.
yes, possible.
for example: imagine both + , = operators invert number. if invert twice - correct result. if invert once (e.g. using non-overloaded = operator) unexpected result.
what happening in case - have no idea. provide not enough data more concrete , useful answer.
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