Question

你好，我试图将我的操作符>>重载到我的班级，但我在eclipse中发出错误信息。

代码：

    friend istream& operator>>(const istream& is, const RAngle& ra){
    return is >> ra.x >> ra.y;
}

码2：

    friend istream& operator>>(const istream& is, const RAngle& ra)
{
    is >> ra.x;
    is >> ra.y;
    return is 
}

两次崩溃，我不知道为什么，请帮助。

编辑：

ra.x＆amp; ra.y是我班级的2个私人投注;

完整错误：

错误：

   ..\/rightangle.h: In function 'std::istream& operator>>(std::istream&, const RAngle&)':
..\/rightangle.h:65:12: error: ambiguous overload for 'operator>>' in 'is >> ra.RAngle::x'
..\/rightangle.h:65:12: note: candidates are:
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:122:7: note: 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>
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:122:7: note:   no known conversion for argument 1 from 'const int' to 'std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&) {aka std::basic_istream<char>& (*)(std::basic_istream<char>&)}'
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:126:7: note: 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>
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:126:7: note:   no known conversion for argument 1 from 'const int' to 'std::basic_istream<char>::__ios_type& (*)(std::basic_istream<char>::__ios_type&) {aka std::basic_ios<char>& (*)(std::basic_ios<char>&)}'
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:133:7: note: 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>
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:133:7: note:   no known conversion for argument 1 from 'const int' to 'std::ios_base& (*)(std::ios_base&)'
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:241:7: note: 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>] <near match>
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:241:7: note:   no known conversion for argument 1 from 'const int' to 'std::basic_istream<char>::__streambuf_type* {aka std::basic_streambuf<char>*}'
..\/rightangle.h:66:12: error: ambiguous overload for 'operator>>' in 'is >> ra.RAngle::y'
..\/rightangle.h:66:12: note: candidates are:
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:122:7: note: 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>
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:122:7: note:   no known conversion for argument 1 from 'const int' to 'std::basic_istream<char>::__istream_type& (*)(std::basic_istream<char>::__istream_type&) {aka std::basic_istream<char>& (*)(std::basic_istream<char>&)}'
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:126:7: note: 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>
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:126:7: note:   no known conversion for argument 1 from 'const int' to 'std::basic_istream<char>::__ios_type& (*)(std::basic_istream<char>::__ios_type&) {aka std::basic_ios<char>& (*)(std::basic_ios<char>&)}'
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:133:7: note: 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>
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:133:7: note:   no known conversion for argument 1 from 'const int' to 'std::ios_base& (*)(std::ios_base&)'
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:241:7: note: 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>] <near match>
c:\mingw\bin\../lib/gcc/mingw32/4.6.1/include/c++/istream:241:7: note:   no known conversion for argument 1 from 'const int' to 'std::basic_istream<char>::__streambuf_type* {aka std::basic_streambuf<char>*}''

Answer 1

一个问题在于运营商的签名：

friend istream& operator>>(const istream& is, const RAngle& ra){
//                         ^^^^^              ^^^^^
    return is >> ra.x >> ra.y;
}

如果参数为const，您将无法修改它们。从错误消息开始，它们似乎表明编译器未能找到is >> ra.x和is >> ra.y的适当重载。这可能与上一个问题有关（无法找到带有const-lvalue的重载），具体取决于ra.x和ra.y的类型（问题中未显示）

Answer 2

由于operator>>将修改传递给它的参数，因此它们不能引用const，所以你想要的是：

friend std::istream &operator>>(std::istream &is, RAngle &ra) { 
    return is >> ra.x >> ra.y;
}

请注意，几乎所有I / O操作（至少可能）都会更改流的状态，因此您（几乎？）总是希望通过非const引用传递流参数。

Answer 3

请从参数＆＃34; const RAngle＆amp;中删除const。 RA＆＃34 ;.您无法修改方法中的常量引用。

与班级的朋友istream操作员

3 个答案: