c++找不到带错误c2678的运算符
c++ No operator found with error c2678
很抱歉发了这么长的帖子，但我不知道是什么原因导致的，我正在自学c++
我试着只使用一个字符串变量，如果输入是c或f，则将其更改为celsius或fahrenheit，但它给出了相同的错误。。
代码：
// Custom.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <iostream>
#include <Windows.h>
#include <String>
int _tmain(int argc, _TCHAR* argv[])
{
using namespace std;
double input, out;
string degtype;
char type ;
cin >> "What is the temperature: " >> input;
cin >> "Convert to [C]elsius or [F]ahrenheit?: " >> type;
if (type=='C' || type=='c')
{
out = (-32 - (input * 1.8)) + input;
degtype = "Celcius";
}
else
if (type=='F' || type=='f')
{
out = 32 + (input * 1.8);
degtype = "Fahrenheit";
}
cout << "The " << degtype << "value is " << out;
}
错误：
1>------ Build started: Project: Custom, Configuration: Debug Win32 ------
1> Custom.cpp
1>c:userscharlesdocumentsvisual studio 2010projectscustomcustomcustom.cpp(18): error C2678: binary '>>' : no operator found which takes a left-hand operand of type 'std::istream' (or there is no acceptable conversion)
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1053): could be 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &&,signed char *)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1060): or 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &&,signed char &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1067): or 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &&,unsigned char *)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1074): or 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &&,unsigned char &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1097): or 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &,signed char *)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1104): or 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &,signed char &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1111): or 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &,unsigned char *)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1118): or 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &,unsigned char &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1128): or 'std::basic_istream<_Elem,_Traits> &std::operator >><char,std::char_traits<char>,const char[26]>(std::basic_istream<_Elem,_Traits> &&,_Ty (&))'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>,
1> _Ty=const char [26]
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(179): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::basic_istream<_Elem,_Traits> &(__cdecl *)(std::basic_istream<_Elem,_Traits> &))'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(185): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::basic_ios<_Elem,_Traits> &(__cdecl *)(std::basic_ios<_Elem,_Traits> &))'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(192): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::ios_base &(__cdecl *)(std::ios_base &))'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(199): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::_Bool &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(218): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(short &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(253): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(unsigned short &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(272): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(int &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(298): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(unsigned int &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(316): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(long &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(334): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(unsigned long &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(354): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(__int64 &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(373): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(unsigned __int64 &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(392): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(float &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(411): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(double &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(429): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(long double &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(447): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(void *&)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(466): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::basic_streambuf<_Elem,_Traits> *)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> while trying to match the argument list '(std::istream, const char [26])'
1>c:userscharlesdocumentsvisual studio 2010projectscustomcustomcustom.cpp(19): error C2678: binary '>>' : no operator found which takes a left-hand operand of type 'std::istream' (or there is no acceptable conversion)
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1053): could be 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &&,signed char *)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1060): or 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &&,signed char &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1067): or 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &&,unsigned char *)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1074): or 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &&,unsigned char &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1097): or 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &,signed char *)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1104): or 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &,signed char &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1111): or 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &,unsigned char *)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1118): or 'std::basic_istream<_Elem,_Traits> &std::operator >><std::char_traits<char>>(std::basic_istream<_Elem,_Traits> &,unsigned char &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(1128): or 'std::basic_istream<_Elem,_Traits> &std::operator >><char,std::char_traits<char>,const char[40]>(std::basic_istream<_Elem,_Traits> &&,_Ty (&))'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>,
1> _Ty=const char [40]
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(179): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::basic_istream<_Elem,_Traits> &(__cdecl *)(std::basic_istream<_Elem,_Traits> &))'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(185): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::basic_ios<_Elem,_Traits> &(__cdecl *)(std::basic_ios<_Elem,_Traits> &))'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(192): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::ios_base &(__cdecl *)(std::ios_base &))'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(199): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::_Bool &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(218): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(short &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(253): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(unsigned short &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(272): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(int &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(298): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(unsigned int &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(316): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(long &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(334): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(unsigned long &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(354): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(__int64 &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(373): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(unsigned __int64 &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(392): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(float &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(411): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(double &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(429): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(long double &)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(447): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(void *&)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> c:program files (x86)microsoft visual studio 10.0vcincludeistream(466): or 'std::basic_istream<_Elem,_Traits> &std::basic_istream<_Elem,_Traits>::operator >>(std::basic_streambuf<_Elem,_Traits> *)'
1> with
1> [
1> _Elem=char,
1> _Traits=std::char_traits<char>
1> ]
1> while trying to match the argument list '(std::istream, const char [40])'
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
cin >> "What is the temperature: " >> input;
应该是
cout << "What is the temperature: ";
cin >> input;
等等
忽略由(cin/cout，请参阅NPE的答案)引起的错误：
评估变量类型
如果您输入除F/F/C/C之外的任何其他内容，您的代码将返回一些胡言乱语，因为out和degtype都没有得到值，除了预设值。您可以通过构建一个评估输出类型的递归函数来解决这个问题，预先定义在无效输入的情况下使用的默认行为，将这种情况处理为错误或将类型初始化为"错误"。
评估递归输入：
#include <string>
#include <list>
using namespace std;
string evalInput(list<string> acceptedStrings, string textToDisplay)
{
cout << textToDisplay << endl;
cin >> input;
if ( any_of(acceptedStrings.begin(),acceptedStrings.end(),(string)input))
{
return input;
}
else
{
cout<<"Invalid input provided, valid inputs are:" << endl;
for each (string s in acceptedStrings){ cout << s << endl;}
evalInput(acceptedStrings,textToDisplay); // calling itself, hence recursive
}
}
处理未定义状态
if (type=='C' || type=='c')
{
out = (-32 - (input * 1.8)) + input;
degtype = "Celcius";
}
else if (type=='F' || type=='f')
{
out = 32 + (input * 1.8);
degtype = "Fahrenheit";
}
else
{
// do whatever you want here, you can inform of a bad input and
// hence using a default behavior, or simply inform of a bad input
// and deny further progress
}
初始化为错误/未初始化
// Preset degtype and out:
degtype = 'E';
out = -999;
现在你必须检查degtype和out提供的值是否是错误的，所以你可以像这样更改最后几行：
if (degtype != 'E')
{
cout << "The " << degtype << "value is " << out;
}
else
{
cout << "Invalid temprature unit provided, hit any key to terminate program" << endl;
double terminate;
cin >> terminate;
}
评估输入
如果您的用户为输入提供了任何无效的值，输入将不接受此值，因此我强烈建议预先设置此值。在向用户询问输入后，您可以评估所提供的值是否有效。最简单的方法是将输入预先设置为-999，并在获得用户输入后检查它是否仍然是-999。由于-999不是有效的温度，任何用户都不太可能提供这种输入。
您可以再次通知错误，也可以使用递归方法再次请求输入。
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