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Full Discussion: C++ operator overloading error
Top Forums Programming C++ operator overloading error Post 303026988 by milhan on Thursday 6th of December 2018 02:10:16 PM
Old 12-06-2018
C++ operator overloading error
hi,
I defined my own String class and overloaded the output operator with
Code:
friend ostream& operator<<(ostream& os, const myString& str);
//overloads the << operator so it can be used to output values of type myString

which works fine. Until I try to execute the following statement:
Code:
// + concatenation operator is already defined for myString
cout << (str4=str2+str) << endl; //This statement concatenates str to str2, then assigns it to str4 and returns str4, right?

And, I get error
Code:
error: no match for ‘operator<<' (operand types are ‘std::ostream' {aka ‘std::basic_ostream<char>'} and ‘void')
  cout << (str4=str2+str) << endl;
  ~~~~~^~~~~~~~~~~~~~~~~~

The above code works fine when I change the concatenation statement as follows:
Code:
str4=str2+str;
cout << str4 << endl;

What did I miss?
 

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LEARN ABOUT DEBIAN

ost_date

ost::Date(3)						     Library Functions Manual						      ost::Date(3)

NAME

       ost::Date -

       The Date class uses a julian date representation of the current year, month, and day.

SYNOPSIS

       #include <numbers.h>

       Inherited by ost::DateNumber, and ost::Datetime.

   Public Member Functions
       Date (time_t tm)
       Date (tm *dt)
       Date (char *str, size_t size=0)
       Date (int year, unsigned month, unsigned day)
       Date ()
       virtual ~Date ()
       int getYear (void) const
       unsigned getMonth (void) const
       unsigned getDay (void) const
       unsigned getDayOfWeek (void) const
       char * getDate (char *buffer) const
       time_t getDate (void) const
       time_t getDate (tm *buf) const
       long getValue (void) const
       void setDate (const char *str, size_t size=0)
       bool isValid (void) const
       operator long () const
       String operator() () const
       Date & operator++ ()
       Date & operator-- ()
       Date & operator+= (const long val)
       Date & operator-= (const long val)
       int operator== (const Date &date)
       int operator!= (const Date &date)
       int operator< (const Date &date)
       int operator<= (const Date &date)
       int operator> (const Date &date)
       int operator>= (const Date &date)
       bool operator! () const

   Protected Member Functions
       void toJulian (long year, long month, long day)
       void fromJulian (char *buf) const
       virtual void update (void)
	   A method to use to 'post' any changed values when shadowing a mixed object class.

   Protected Attributes
       long julian

   Friends
       Date operator+ (const Date &date, const long val)
       Date operator- (const Date &date, const long val)
       Date operator+ (const long val, const Date &date)
       Date operator- (const long val, const Date &date)

Detailed Description
       The Date class uses a julian date representation of the current year, month, and day.

       This is then manipulated in several forms and may be exported as needed.

       Author:
	   David Sugar dyfet@ostel.com julian number based date class.

Constructor &; Destructor Documentation
   ost::Date::Date (time_ttm)
   ost::Date::Date (tm *dt)
   ost::Date::Date (char *str, size_tsize = 0)
   ost::Date::Date (intyear, unsignedmonth, unsignedday)
   ost::Date::Date ()
   virtual ost::Date::~Date () [virtual]
Member Function Documentation
   void ost::Date::fromJulian (char *buf) const [protected]
   char* ost::Date::getDate (char *buffer) const
   time_t ost::Date::getDate (void) const
   time_t ost::Date::getDate (tm *buf) const
   unsigned ost::Date::getDay (void) const
   unsigned ost::Date::getDayOfWeek (void) const
   unsigned ost::Date::getMonth (void) const
   long ost::Date::getValue (void) const
   int ost::Date::getYear (void) const
   bool ost::Date::isValid (void) const
       Reimplemented in ost::Datetime.

   ost::Date::operator long () const [inline]
   bool ost::Date::operator! (void) const [inline]
       Reimplemented in ost::Datetime.

   int ost::Date::operator!= (const Date &date)
   String ost::Date::operator() () const
   Date& ost::Date::operator++ ()
   Date& ost::Date::operator+= (const longval)
   Date& ost::Date::operator-- ()
   Date& ost::Date::operator-= (const longval)
   int ost::Date::operator< (const Date &date)
   int ost::Date::operator<= (const Date &date)
   int ost::Date::operator== (const Date &date)
   int ost::Date::operator> (const Date &date)
   int ost::Date::operator>= (const Date &date)
   void ost::Date::setDate (const char *str, size_tsize = 0)
   void ost::Date::toJulian (longyear, longmonth, longday) [protected]
   virtual void ost::Date::update (void) [protected],  [virtual]
       A method to use to 'post' any changed values when shadowing a mixed object class. This is used by DateNumber.

       Reimplemented in ost::DateNumber.

Friends And Related Function Documentation
   Date operator+ (const Date &date, const longval) [friend]
   Date operator+ (const longval, const Date &date) [friend]
   Date operator- (const Date &date, const longval) [friend]
   Date operator- (const longval, const Date &date) [friend]
Member Data Documentation
   long ost::Date::julian [protected]
Author
       Generated automatically by Doxygen for GNU CommonC++ from the source code.

GNU CommonC++							  Sat Jun 23 2012						      ost::Date(3)
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