我在重载运算符“>>”时遇到问题，我不知道发生了什么
I had a problem when overloading the operator ">>" and i don't have any idea what is going on
我已经阅读了对类似问题的其他回复，但没有任何效果。这些回复建议包括 #include <string>，但这没有用。此外，我尝试在 User class 中创建重载 friend 函数，但没有成功。
这是User class:
class User
{
bool status;
std::string first_name;
std::string last_name;
public:
static int user_count;
User()
{
status = 0;
first_name = "first";
last_name = "last";
user_count++;
}
User(std::string new_first, std::string new_last, bool new_status)
{
first_name = new_first;
last_name = new_last;
status = new_status;
user_count++;
}
//Some getters and setters...
~User()
{
user_count--;
}
friend std::ostream& operator <<(std::ostream&, User&);
friend std::istream& operator >>(std::istream&, User&);
};
是的，我在 class 之外初始化了 user_count。
这些是重载：
std::ostream& operator <<(std::ostream& output, User& user)
{
output << "First name: " << user.first_name << "\nLast name: " << user.last_name;
return output;
}
std::istream& operator >>(std::istream& input, User& user)
{
input >> user.first_name >> user.last_name >> user.status;
return input;
}
这是main()函数：
int main()
{
User user();
std::cin >> user;
std::cout << user << std::endl;
return EXIT_SUCCESS;
}
headers 是：
#include <iostream>
#include <string>
编辑：我没有很好地解释自己。我正在关注 YouTube 上关于运算符重载的教程，我正在复制视频中那个人正在做的事情，<< 上的重载工作正常，但是当我尝试在 >> 上这样做时，我得到这个巨大的错误：
main.cpp: In function ‘int main()’:
main.cpp:75:14: error: no match for ‘operator>>’ (operand types are ‘std::istream’ {aka ‘std::basic_istream<char>’} and ‘User(’)
75 | std::cin >> user;
| ~~~~~~~~ ^~ ~~~~
| | |
| | User()
| std::istream {aka std::basic_istream<char>}
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:120:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__istream_type& (*)(std::basic_istream<_CharT, _Traits>::__istream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
120 | operator>>(__istream_type& (*__pf)(__istream_type&))
| ^~~~~~~~
/usr/include/c++/9/istream:120:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&)’ {aka ‘std::basic_istream<char>& (*)(std::basic_istream<char>&)’} [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:124:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__ios_type& (*)(std::basic_istream<_CharT, _Traits>::__ios_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>; std::basic_istream<_CharT, _Traits>::__ios_type = std::basic_ios<char>]’ <near match>
124 | operator>>(__ios_type& (*__pf)(__ios_type&))
| ^~~~~~~~
/usr/include/c++/9/istream:124:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘std::basic_istream<char>::__ios_type& (*)(std::basic_istream<char>::__ios_type&)’ {aka ‘std::basic_ios<char>& (*)(std::basic_ios<char>&)’} [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:131:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::ios_base& (*)(std::ios_base&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
131 | operator>>(ios_base& (*__pf)(ios_base&))
| ^~~~~~~~
/usr/include/c++/9/istream:131:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘std::ios_base& (*)(std::ios_base&)’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:168:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(bool&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
168 | operator>>(bool& __n)
| ^~~~~~~~
/usr/include/c++/9/istream:168:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: cannot bind non-const lvalue reference of type ‘bool&’ to an rvalue of type ‘bool’
75 | std::cin >> user;
| ^~~~
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:172:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(short int&) [with _CharT = char; _Traits = std::char_traits<char>]’ <near match>
172 | operator>>(short& __n);
| ^~~~~~~~
/usr/include/c++/9/istream:172:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘short int’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(short int)user’ to ‘short int&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:175:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(short unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
175 | operator>>(unsigned short& __n)
| ^~~~~~~~
/usr/include/c++/9/istream:175:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘short unsigned int’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(short unsigned int)user’ to ‘short unsigned int&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:179:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(int&) [with _CharT = char; _Traits = std::char_traits<char>]’ <near match>
179 | operator>>(int& __n);
| ^~~~~~~~
/usr/include/c++/9/istream:179:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘int’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(int)user’ to ‘int&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:182:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
182 | operator>>(unsigned int& __n)
| ^~~~~~~~
/usr/include/c++/9/istream:182:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘unsigned int’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(unsigned int)user’ to ‘unsigned int&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:186:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
186 | operator>>(long& __n)
| ^~~~~~~~
/usr/include/c++/9/istream:186:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘long int’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(long int)user’ to ‘long int&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:190:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
190 | operator>>(unsigned long& __n)
| ^~~~~~~~
/usr/include/c++/9/istream:190:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘long unsigned int’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(long unsigned int)user’ to ‘long unsigned int&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:195:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
195 | operator>>(long long& __n)
| ^~~~~~~~
/usr/include/c++/9/istream:195:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘long long int’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(long long int)user’ to ‘long long int&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:199:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
199 | operator>>(unsigned long long& __n)
| ^~~~~~~~
/usr/include/c++/9/istream:199:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘long long unsigned int’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(long long unsigned int)user’ to ‘long long unsigned int&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:235:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(void*&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
235 | operator>>(void*& __p)
| ^~~~~~~~
/usr/include/c++/9/istream:235:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘void*’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(void*)user’ to ‘void*&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:214:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(float&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’
214 | operator>>(float& __f)
| ^~~~~~~~
/usr/include/c++/9/istream:214:25: note: no known conversion for argument 1 from ‘User()’ to ‘float&’
214 | operator>>(float& __f)
| ~~~~~~~^~~
/usr/include/c++/9/istream:218:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(double&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’
218 | operator>>(double& __f)
| ^~~~~~~~
/usr/include/c++/9/istream:218:26: note: no known conversion for argument 1 from ‘User()’ to ‘double&’
218 | operator>>(double& __f)
| ~~~~~~~~^~~
/usr/include/c++/9/istream:222:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long double&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’
222 | operator>>(long double& __f)
| ^~~~~~~~
/usr/include/c++/9/istream:222:31: note: no known conversion for argument 1 from ‘User()’ to ‘long double&’
222 | operator>>(long double& __f)
| ~~~~~~~~~~~~~^~~
/usr/include/c++/9/istream:259:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__streambuf_type*) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__streambuf_type = std::basic_streambuf<char>]’
259 | operator>>(__streambuf_type* __sb);
| ^~~~~~~~
/usr/include/c++/9/istream:259:36: note: no known conversion for argument 1 from ‘User()’ to ‘std::basic_istream<char>::__streambuf_type*’ {aka ‘std::basic_streambuf<char>*’}
259 | operator>>(__streambuf_type* __sb);
| ~~~~~~~~~~~~~~~~~~^~~~
main.cpp:65:15: note: candidate: ‘std::istream& operator>>(std::istream&, User&)’
65 | std::istream& operator >>(std::istream& input, User& user)
| ^~~~~~~~
main.cpp:65:54: note: no known conversion for argument 2 from ‘User()’ to ‘User&’
65 | std::istream& operator >>(std::istream& input, User& user)
| ~~~~~~^~~~
In file included from /usr/include/c++/9/string:56,
from /usr/include/c++/9/bits/locale_classes.h:40,
from /usr/include/c++/9/bits/ios_base.h:41,
from /usr/include/c++/9/ios:42,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from main.cpp:1:
/usr/include/c++/9/bits/basic_string.tcc:1466:5: note: candidate: ‘template<class _CharT, class _Traits, class _Alloc> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)’
1466 | operator>>(basic_istream<_CharT, _Traits>& __in,
| ^~~~~~~~
/usr/include/c++/9/bits/basic_string.tcc:1466:5: note: template argument deduction/substitution failed:
main.cpp:75:17: note: mismatched types ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>’ and ‘User()’
75 | std::cin >> user;
| ^~~~
In file included from /usr/include/c++/9/istream:991,
from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/bits/istream.tcc:931:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, _CharT&)’
931 | operator>>(basic_istream<_CharT, _Traits>& __in, _CharT& __c)
| ^~~~~~~~
/usr/include/c++/9/bits/istream.tcc:931:5: note: template argument deduction/substitution failed:
main.cpp:75:17: note: deduced conflicting types for parameter ‘_CharT’ (‘char’ and ‘User()’)
75 | std::cin >> user;
| ^~~~
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:756:5: note: candidate: ‘template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, unsigned char&)’
756 | operator>>(basic_istream<char, _Traits>& __in, unsigned char& __c)
| ^~~~~~~~
/usr/include/c++/9/istream:756:5: note: template argument deduction/substitution failed:
main.cpp:75:17: note: cannot convert ‘user’ (type ‘User()’) to type ‘unsigned char&’
75 | std::cin >> user;
| ^~~~
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:761:5: note: candidate: ‘template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, signed char&)’
761 | operator>>(basic_istream<char, _Traits>& __in, signed char& __c)
| ^~~~~~~~
/usr/include/c++/9/istream:761:5: note: template argument deduction/substitution failed:
main.cpp:75:17: note: cannot convert ‘user’ (type ‘User()’) to type ‘signed char&’
75 | std::cin >> user;
| ^~~~
In file included from /usr/include/c++/9/istream:991,
from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/bits/istream.tcc:963:5: note: candidate: ‘template<class _CharT2, class _Traits2> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, _CharT2*)’
963 | operator>>(basic_istream<_CharT, _Traits>& __in, _CharT* __s)
| ^~~~~~~~
/usr/include/c++/9/bits/istream.tcc:963:5: note: template argument deduction/substitution failed:
main.cpp:75:17: note: deduced conflicting types for parameter ‘_CharT2’ (‘char’ and ‘User()’)
75 | std::cin >> user;
| ^~~~
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:803:5: note: candidate: ‘template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, unsigned char*)’
803 | operator>>(basic_istream<char, _Traits>& __in, unsigned char* __s)
| ^~~~~~~~
/usr/include/c++/9/istream:803:5: note: template argument deduction/substitution failed:
main.cpp:75:17: note: cannot convert ‘user’ (type ‘User()’) to type ‘unsigned char*’
75 | std::cin >> user;
| ^~~~
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:808:5: note: candidate: ‘template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, signed char*)’
808 | operator>>(basic_istream<char, _Traits>& __in, signed char* __s)
| ^~~~~~~~
/usr/include/c++/9/istream:808:5: note: template argument deduction/substitution failed:
main.cpp:75:17: note: cannot convert ‘user’ (type ‘User()’) to type ‘signed char*’
75 | std::cin >> user;
| ^~~~
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:980:5: note: candidate: ‘template<class _Istream, class _Tp> typename std::enable_if<std::__and_<std::__not_<std::is_lvalue_reference<_Tp> >, std::__is_convertible_to_basic_istream<_Istream>, std::__is_extractable<typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type, _Tp&&, void> >::value, typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type>::type std::operator>>(_Istream&&, _Tp&&)’
980 | operator>>(_Istream&& __is, _Tp&& __x)
| ^~~~~~~~
/usr/include/c++/9/istream:980:5: note: template argument deduction/substitution failed:
/usr/include/c++/9/istream: In substitution of ‘template<class _Istream, class _Tp> typename std::enable_if<std::__and_<std::__not_<std::is_lvalue_reference<_Tp> >, std::__is_convertible_to_basic_istream<_Istream>, std::__is_extractable<typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type, _Tp&&, void> >::value, typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type>::type std::operator>>(_Istream&&, _Tp&&) [with _Istream = std::basic_istream<char>&; _Tp = User (&)()]’:
main.cpp:75:17: required from here
/usr/include/c++/9/istream:980:5: error: no type named ‘type’ in ‘struct std::enable_if<false, std::basic_istream<char>&>’
希望对您有所帮助。
在 main() 中，User user(); 声明了一个名为 user 的 函数 并且 returns 声明了一个 User.在这种情况下，这不是您想要的。您需要一个 对象实例 来代替。因此，您需要从声明中删除括号，例如： User user; 它声明了一个名为 user 且类型为 User 的 变量 ，然后调用它的默认构造函数。
此外，在 operator<< 中，第二个参数应该声明为 const User& user。
我已经阅读了对类似问题的其他回复，但没有任何效果。这些回复建议包括 #include <string>，但这没有用。此外，我尝试在 User class 中创建重载 friend 函数，但没有成功。
这是User class:
class User
{
bool status;
std::string first_name;
std::string last_name;
public:
static int user_count;
User()
{
status = 0;
first_name = "first";
last_name = "last";
user_count++;
}
User(std::string new_first, std::string new_last, bool new_status)
{
first_name = new_first;
last_name = new_last;
status = new_status;
user_count++;
}
//Some getters and setters...
~User()
{
user_count--;
}
friend std::ostream& operator <<(std::ostream&, User&);
friend std::istream& operator >>(std::istream&, User&);
};
是的，我在 class 之外初始化了 user_count。
这些是重载：
std::ostream& operator <<(std::ostream& output, User& user)
{
output << "First name: " << user.first_name << "\nLast name: " << user.last_name;
return output;
}
std::istream& operator >>(std::istream& input, User& user)
{
input >> user.first_name >> user.last_name >> user.status;
return input;
}
这是main()函数：
int main()
{
User user();
std::cin >> user;
std::cout << user << std::endl;
return EXIT_SUCCESS;
}
headers 是：
#include <iostream>
#include <string>
编辑：我没有很好地解释自己。我正在关注 YouTube 上关于运算符重载的教程，我正在复制视频中那个人正在做的事情，<< 上的重载工作正常，但是当我尝试在 >> 上这样做时，我得到这个巨大的错误：
main.cpp: In function ‘int main()’:
main.cpp:75:14: error: no match for ‘operator>>’ (operand types are ‘std::istream’ {aka ‘std::basic_istream<char>’} and ‘User(’)
75 | std::cin >> user;
| ~~~~~~~~ ^~ ~~~~
| | |
| | User()
| std::istream {aka std::basic_istream<char>}
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:120:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__istream_type& (*)(std::basic_istream<_CharT, _Traits>::__istream_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
120 | operator>>(__istream_type& (*__pf)(__istream_type&))
| ^~~~~~~~
/usr/include/c++/9/istream:120:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&)’ {aka ‘std::basic_istream<char>& (*)(std::basic_istream<char>&)’} [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:124:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__ios_type& (*)(std::basic_istream<_CharT, _Traits>::__ios_type&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>; std::basic_istream<_CharT, _Traits>::__ios_type = std::basic_ios<char>]’ <near match>
124 | operator>>(__ios_type& (*__pf)(__ios_type&))
| ^~~~~~~~
/usr/include/c++/9/istream:124:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘std::basic_istream<char>::__ios_type& (*)(std::basic_istream<char>::__ios_type&)’ {aka ‘std::basic_ios<char>& (*)(std::basic_ios<char>&)’} [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:131:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(std::ios_base& (*)(std::ios_base&)) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
131 | operator>>(ios_base& (*__pf)(ios_base&))
| ^~~~~~~~
/usr/include/c++/9/istream:131:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘std::ios_base& (*)(std::ios_base&)’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:168:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(bool&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
168 | operator>>(bool& __n)
| ^~~~~~~~
/usr/include/c++/9/istream:168:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: cannot bind non-const lvalue reference of type ‘bool&’ to an rvalue of type ‘bool’
75 | std::cin >> user;
| ^~~~
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:172:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(short int&) [with _CharT = char; _Traits = std::char_traits<char>]’ <near match>
172 | operator>>(short& __n);
| ^~~~~~~~
/usr/include/c++/9/istream:172:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘short int’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(short int)user’ to ‘short int&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:175:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(short unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
175 | operator>>(unsigned short& __n)
| ^~~~~~~~
/usr/include/c++/9/istream:175:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘short unsigned int’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(short unsigned int)user’ to ‘short unsigned int&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:179:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(int&) [with _CharT = char; _Traits = std::char_traits<char>]’ <near match>
179 | operator>>(int& __n);
| ^~~~~~~~
/usr/include/c++/9/istream:179:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘int’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(int)user’ to ‘int&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:182:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
182 | operator>>(unsigned int& __n)
| ^~~~~~~~
/usr/include/c++/9/istream:182:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘unsigned int’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(unsigned int)user’ to ‘unsigned int&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:186:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
186 | operator>>(long& __n)
| ^~~~~~~~
/usr/include/c++/9/istream:186:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘long int’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(long int)user’ to ‘long int&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:190:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
190 | operator>>(unsigned long& __n)
| ^~~~~~~~
/usr/include/c++/9/istream:190:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘long unsigned int’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(long unsigned int)user’ to ‘long unsigned int&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:195:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
195 | operator>>(long long& __n)
| ^~~~~~~~
/usr/include/c++/9/istream:195:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘long long int’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(long long int)user’ to ‘long long int&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:199:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long long unsigned int&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
199 | operator>>(unsigned long long& __n)
| ^~~~~~~~
/usr/include/c++/9/istream:199:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘long long unsigned int’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(long long unsigned int)user’ to ‘long long unsigned int&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:235:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(void*&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’ <near match>
235 | operator>>(void*& __p)
| ^~~~~~~~
/usr/include/c++/9/istream:235:7: note: conversion of argument 1 would be ill-formed:
main.cpp:75:17: error: invalid conversion from ‘User (*)()’ to ‘void*’ [-fpermissive]
75 | std::cin >> user;
| ^~~~
| |
| User (*)()
main.cpp:75:17: error: cannot bind rvalue ‘(void*)user’ to ‘void*&’
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:214:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(float&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’
214 | operator>>(float& __f)
| ^~~~~~~~
/usr/include/c++/9/istream:214:25: note: no known conversion for argument 1 from ‘User()’ to ‘float&’
214 | operator>>(float& __f)
| ~~~~~~~^~~
/usr/include/c++/9/istream:218:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(double&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’
218 | operator>>(double& __f)
| ^~~~~~~~
/usr/include/c++/9/istream:218:26: note: no known conversion for argument 1 from ‘User()’ to ‘double&’
218 | operator>>(double& __f)
| ~~~~~~~~^~~
/usr/include/c++/9/istream:222:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>::__istream_type& std::basic_istream<_CharT, _Traits>::operator>>(long double&) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__istream_type = std::basic_istream<char>]’
222 | operator>>(long double& __f)
| ^~~~~~~~
/usr/include/c++/9/istream:222:31: note: no known conversion for argument 1 from ‘User()’ to ‘long double&’
222 | operator>>(long double& __f)
| ~~~~~~~~~~~~~^~~
/usr/include/c++/9/istream:259:7: note: candidate: ‘std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>::__streambuf_type*) [with _CharT = char; _Traits = std::char_traits<char>; std::basic_istream<_CharT, _Traits>::__streambuf_type = std::basic_streambuf<char>]’
259 | operator>>(__streambuf_type* __sb);
| ^~~~~~~~
/usr/include/c++/9/istream:259:36: note: no known conversion for argument 1 from ‘User()’ to ‘std::basic_istream<char>::__streambuf_type*’ {aka ‘std::basic_streambuf<char>*’}
259 | operator>>(__streambuf_type* __sb);
| ~~~~~~~~~~~~~~~~~~^~~~
main.cpp:65:15: note: candidate: ‘std::istream& operator>>(std::istream&, User&)’
65 | std::istream& operator >>(std::istream& input, User& user)
| ^~~~~~~~
main.cpp:65:54: note: no known conversion for argument 2 from ‘User()’ to ‘User&’
65 | std::istream& operator >>(std::istream& input, User& user)
| ~~~~~~^~~~
In file included from /usr/include/c++/9/string:56,
from /usr/include/c++/9/bits/locale_classes.h:40,
from /usr/include/c++/9/bits/ios_base.h:41,
from /usr/include/c++/9/ios:42,
from /usr/include/c++/9/ostream:38,
from /usr/include/c++/9/iostream:39,
from main.cpp:1:
/usr/include/c++/9/bits/basic_string.tcc:1466:5: note: candidate: ‘template<class _CharT, class _Traits, class _Alloc> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&)’
1466 | operator>>(basic_istream<_CharT, _Traits>& __in,
| ^~~~~~~~
/usr/include/c++/9/bits/basic_string.tcc:1466:5: note: template argument deduction/substitution failed:
main.cpp:75:17: note: mismatched types ‘std::__cxx11::basic_string<_CharT, _Traits, _Alloc>’ and ‘User()’
75 | std::cin >> user;
| ^~~~
In file included from /usr/include/c++/9/istream:991,
from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/bits/istream.tcc:931:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, _CharT&)’
931 | operator>>(basic_istream<_CharT, _Traits>& __in, _CharT& __c)
| ^~~~~~~~
/usr/include/c++/9/bits/istream.tcc:931:5: note: template argument deduction/substitution failed:
main.cpp:75:17: note: deduced conflicting types for parameter ‘_CharT’ (‘char’ and ‘User()’)
75 | std::cin >> user;
| ^~~~
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:756:5: note: candidate: ‘template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, unsigned char&)’
756 | operator>>(basic_istream<char, _Traits>& __in, unsigned char& __c)
| ^~~~~~~~
/usr/include/c++/9/istream:756:5: note: template argument deduction/substitution failed:
main.cpp:75:17: note: cannot convert ‘user’ (type ‘User()’) to type ‘unsigned char&’
75 | std::cin >> user;
| ^~~~
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:761:5: note: candidate: ‘template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, signed char&)’
761 | operator>>(basic_istream<char, _Traits>& __in, signed char& __c)
| ^~~~~~~~
/usr/include/c++/9/istream:761:5: note: template argument deduction/substitution failed:
main.cpp:75:17: note: cannot convert ‘user’ (type ‘User()’) to type ‘signed char&’
75 | std::cin >> user;
| ^~~~
In file included from /usr/include/c++/9/istream:991,
from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/bits/istream.tcc:963:5: note: candidate: ‘template<class _CharT2, class _Traits2> std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, _CharT2*)’
963 | operator>>(basic_istream<_CharT, _Traits>& __in, _CharT* __s)
| ^~~~~~~~
/usr/include/c++/9/bits/istream.tcc:963:5: note: template argument deduction/substitution failed:
main.cpp:75:17: note: deduced conflicting types for parameter ‘_CharT2’ (‘char’ and ‘User()’)
75 | std::cin >> user;
| ^~~~
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:803:5: note: candidate: ‘template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, unsigned char*)’
803 | operator>>(basic_istream<char, _Traits>& __in, unsigned char* __s)
| ^~~~~~~~
/usr/include/c++/9/istream:803:5: note: template argument deduction/substitution failed:
main.cpp:75:17: note: cannot convert ‘user’ (type ‘User()’) to type ‘unsigned char*’
75 | std::cin >> user;
| ^~~~
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:808:5: note: candidate: ‘template<class _Traits> std::basic_istream<char, _Traits>& std::operator>>(std::basic_istream<char, _Traits>&, signed char*)’
808 | operator>>(basic_istream<char, _Traits>& __in, signed char* __s)
| ^~~~~~~~
/usr/include/c++/9/istream:808:5: note: template argument deduction/substitution failed:
main.cpp:75:17: note: cannot convert ‘user’ (type ‘User()’) to type ‘signed char*’
75 | std::cin >> user;
| ^~~~
In file included from /usr/include/c++/9/iostream:40,
from main.cpp:1:
/usr/include/c++/9/istream:980:5: note: candidate: ‘template<class _Istream, class _Tp> typename std::enable_if<std::__and_<std::__not_<std::is_lvalue_reference<_Tp> >, std::__is_convertible_to_basic_istream<_Istream>, std::__is_extractable<typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type, _Tp&&, void> >::value, typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type>::type std::operator>>(_Istream&&, _Tp&&)’
980 | operator>>(_Istream&& __is, _Tp&& __x)
| ^~~~~~~~
/usr/include/c++/9/istream:980:5: note: template argument deduction/substitution failed:
/usr/include/c++/9/istream: In substitution of ‘template<class _Istream, class _Tp> typename std::enable_if<std::__and_<std::__not_<std::is_lvalue_reference<_Tp> >, std::__is_convertible_to_basic_istream<_Istream>, std::__is_extractable<typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type, _Tp&&, void> >::value, typename std::__is_convertible_to_basic_istream<_Tp>::__istream_type>::type std::operator>>(_Istream&&, _Tp&&) [with _Istream = std::basic_istream<char>&; _Tp = User (&)()]’:
main.cpp:75:17: required from here
/usr/include/c++/9/istream:980:5: error: no type named ‘type’ in ‘struct std::enable_if<false, std::basic_istream<char>&>’
希望对您有所帮助。
在 main() 中，User user(); 声明了一个名为 user 的 函数 并且 returns 声明了一个 User.在这种情况下，这不是您想要的。您需要一个 对象实例 来代替。因此，您需要从声明中删除括号，例如： User user; 它声明了一个名为 user 且类型为 User 的 变量 ，然后调用它的默认构造函数。
此外，在 operator<< 中，第二个参数应该声明为 const User& user。