类异常和运算符答案

【问题标题】：Classes Exceptions and Operators类异常和运算符
【发布时间】：2013-07-29 04:52:54
【问题描述】：

我在让很多操作员工作时遇到了一些麻烦

赋值指令如下

此作业的目的是处理异常。如你所愿回想一下，我为您提供了一个名为 FlashDrive 的示例类，它如下图所示。您可以获取源此处的 FlashDrive 类（.NET 或 .NET 2010）我希望您加强此类，以便调用其方法或运算符可能会抛出异常，而不仅仅是将错误消息打印到 cout。目前，我们最喜欢的异常类是 std::logic_error。你可以通过将字符串值传递给其构造函数来创建 logic_error。正式地，您还应该说#include 开始工作使用 logic_error，但 Visual Studio（作为一个行为不端的孩子......）让你摆脱它。一旦你让一切正常工作，驱动程序代码应该按照类中的描述运行。

尽管示例驱动程序代码可能无法针对所有这些在以下情况下，我希望您在以下情况下抛出异常：

放入驱动器的东西超过了它可以安全容纳的东西（由于写数据）

负数可能用作 my_StorageUsed 值（由于 to operator - 或者错误的值被发送到构造函数调用）

负数可能用作 my_StorageCapacity 值（由于操作员 - 或错误的值被发送到构造函数调用）因此，请仔细遍历所有运算符和方法确保在这些中的每一个中都抛出 logic_error 的类情况。

我还希望您让操作员 > 为类闪存驱动器。最后，我希望你将 FlashDrive 放入命名空间 cs52。

下面是我的代码和构建输出

FlashDrive.h

#ifndef FLASHDRIVE_H
#define FLASHDRIVE_H
#include <iostream>
#include <cstdlib>

namespace cs52 {

class FlashDrive {
    friend FlashDrive operator+ (FlashDrive used1 , FlashDrive used2);
    friend FlashDrive operator- (FlashDrive used3, FlashDrive used4 );

public:

    FlashDrive& FlashDrive::operator=(int);
    FlashDrive::FlashDrive(int);
    FlashDrive& operator = (const FlashDrive& usedtotal){
        my_StorageUsed= usedtotal.my_StorageUsed;
        return *this;
    }
    FlashDrive( );
    FlashDrive( int capacity, int used, bool pluggedIn );

    void plugIn( );
    void pullOut( );
    void writeData( int amount );
    void eraseData( int amount );
    void formatDrive( );

    int  getCapacity( );
    void setCapacity( int amount );
    int  getUsed( );
    void setUsed( int amount );
    bool isPluggedIn( );

private:
    int my_StorageCapacity;   // in kilobytes
    int my_StorageUsed;       // in kilobytes
    bool my_IsPluggedIn;      // am I attached to a computer?
}extern drive1,drive2;

inline FlashDrive operator+ (FlashDrive used1, FlashDrive used2 ) {

    FlashDrive plus;

    plus.my_StorageUsed = (used1.getUsed()+ used2.getUsed());
    return plus;
}
inline bool operator< (FlashDrive &lhs,FlashDrive &rhs ) {
   return ( lhs.getUsed() < rhs.getUsed() );
}
inline bool operator> (FlashDrive &lhs,FlashDrive &rhs ) {
   return ( operator <( rhs, lhs ) );
}
inline FlashDrive operator - (FlashDrive used3, FlashDrive used4 ){
    FlashDrive minus;
    minus.my_StorageUsed = (used3.getUsed()- used4.getUsed());
    return minus;
};

}
#endif

FlashDrive.cpp

#include <iostream>
#include <cstdlib>
#include "FlashDrive.h"

namespace cs52 {

FlashDrive::FlashDrive( ) {
  my_StorageCapacity = 0;
  my_StorageUsed = 0;
  my_IsPluggedIn = false;
}
FlashDrive::FlashDrive( int capacity, int used, bool pluggedIn ) { 
  my_StorageCapacity = capacity;
  my_StorageUsed = used;
  my_IsPluggedIn = pluggedIn;
}
void FlashDrive::plugIn( ) {
  my_IsPluggedIn = true;
}
void FlashDrive::pullOut( ) {
  my_IsPluggedIn = false;
}
void FlashDrive::writeData( int amount ) {
  my_StorageUsed += amount;
}
void FlashDrive::eraseData( int amount ) {
  my_StorageUsed -= amount;
}
void FlashDrive::formatDrive( ) {
  my_StorageUsed = 0;
}

int  FlashDrive::getCapacity( ) {
  return( my_StorageCapacity );
}
void FlashDrive::setCapacity( int amount ) {
  my_StorageCapacity = amount;
}
int  FlashDrive::getUsed( ) {
  return( my_StorageUsed );
}
void FlashDrive::setUsed( int amount ) {
  my_StorageUsed = amount;
}
bool FlashDrive::isPluggedIn( ) {
  return( my_IsPluggedIn );
}
}

Main.cpp

#include <iostream>
#include <cstdlib>
#include "FlashDrive.h"
void main( )
{
using namespace cs52;
cs52::FlashDrive empty;
cs52::FlashDrive drive1( 10, 0, false );
cs52::FlashDrive drive2( 20, 0, false );

drive1.plugIn( );
drive1.formatDrive( );
drive1.writeData( 5 );
drive1.pullOut( );

drive2.plugIn( );
drive2.formatDrive( );
drive2.writeData( 1 );
drive2.pullOut( );

// read in a FlashDrive... 
// the class designer for FlashDrive (that's you!)
// gets to decide which fields matter and should be read in
cs52::FlashDrive sample;
cin >> sample;

// print out a FlashDrive...
// the class designer for FlashDrive (that's you!)
// gets to decide which fields matter and should be printed
cout << sample << endl;

cs52::FlashDrive combined = drive1 + drive2;
cout << "this drive's filled to " << combined.getUsed( ) << endl;

cs52::FlashDrive other = combined – drive1;
cout << "the other cup's filled to " << other.getUsed( ) << endl;

if (combined > other) {
  cout << "looks like combined is bigger..." << endl;
}
else {
  cout << "looks like other is bigger..." << endl;
}

if (drive2 > other) {
  cout << "looks like drive2 is bigger..." << endl;
}
else {
  cout << "looks like other is bigger..." << endl;
}

if (drive2 < drive1) {
  cout << "looks like drive2 is smaller..." << endl;
}
else {
  cout << "looks like drive1 is smaller..." << endl;
}

// let's throw some exceptions...

try {
  empty = empty - combined;
  cout << "something not right here..." << endl;
} catch( std::logic_error ) {
// an exception should get thrown... 
// so the lines of code here should
// be run, not the cout statement...
}

try {
  drive2.writeData( 10000 );
  cout << "something not right here..." << endl;
} catch( std::logic_error ) {
// an exception should get thrown... 
// so the lines of code here should
// be run, not the cout statement...
}

try {
  cs52::FlashDrive f( -1, -1, false );
  cout << "something not right here..." << endl;
} catch( std::logic_error ) {
// an exception should get thrown... 
// so the lines of code here should
// be run, not the cout statement...
}
}

我收到一条非常奇怪的错误消息

------ 构建开始：项目：FlashDriver，配置：调试 Win32 ------ 构建开始于 2013 年 7 月 29 日凌晨 4:48:43。 InitializeBuildStatus：触摸“Debug\FlashDriver.unsuccessfulbuild”。 Cl编译：Main.cpp c:\文档和设置\管理员\我的文档\visual studio 2010\projects\flashdriver\flashdriver\main.cpp(28)：错误 C2678： binary '>>' : 没有找到接受左操作数的运算符输入“std::istream”（或者没有可接受的转换） c:\program files\microsoft visual studio 10.0\vc\include\istream(1053): 可能是 'std::basic_istream<_elem> &std::operator

>(std::basic_istream<_elem> &&,signed char *)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(1060): 或 'std::basic_istream<_elem> &std::operator >(std::basic_istream<_elem> &&,signed char &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(1067): 或 'std::basic_istream<_elem> &std::operator >(std::basic_istream<_elem> &&,unsigned char *)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(1074): 或 'std::basic_istream<_elem> &std::operator >(std::basic_istream<_elem> &&,unsigned char &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(1097): 或 'std::basic_istream<_elem> &std::operator >(std::basic_istream<_elem> &,signed char *)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(1104): 或 'std::basic_istream<_elem> &std::operator >(std::basic_istream<_elem> &,signed char &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(1111): 或 'std::basic_istream<_elem> &std::operator >(std::basic_istream<_elem> &,unsigned char *)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(1118): 或 'std::basic_istream<_elem> &std::operator >(std::basic_istream<_elem> &,unsigned char &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(1128): 或 'std::basic_istream<_elem> &std::operator ,cs52::FlashDrive>(std::basic_istream<_elem> &&,_Ty &)' 和 [ _Elem=char, _Traits=std::char_traits, _Ty=cs52::闪存盘 ] c:\program files\microsoft visual studio 10.0\vc\include\istream(179): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>::operator (std::basic_istream<_elem>Traits> &(_cdecl *)(std::basic_istream<_elem> &))' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(185): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>::operator (std::basic_ios<_elem>Traits> &(_cdecl *)(std::basic_ios<_elem> &))' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(192): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>::operator >>(std::ios_base &(__cdecl *)(std::ios_base &))' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(199): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>::operator >>(std::_Bool &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(218): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>::operator >>(short &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(253): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>::operator >>(unsigned short &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(272): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>::operator >>(int &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(298): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>::operator >>(unsigned int &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(316): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>::operator >>(long &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(334): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>::operator >>(unsigned long &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(354): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>特征>::operator >>(_int64 &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(373): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>::operator >>(unsigned __int64 &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(392): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>::operator >>(float &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(411): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>::operator >>(double &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(429): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>::operator >>(long double &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(447): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>::operator >>(void *&)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\istream(466): 或 'std::basic_istream<_elem> &std::basic_istream<_elem>::operator (std::basic_streambuf<_elem> *)' 和 [ _Elem=char, _Traits=std::char_traits ] 在尝试匹配参数列表 '(std::istream, cs52::FlashDrive)' c:\documents and settings\administrator\my 文件\视觉工作室 2010\projects\flashdriver\flashdriver\main.cpp(33)：错误 C2679：二进制 ' &std::operator (std::basic_ostream<_elem> &,const 字符 *)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\ostream(726): 或 'std::basic_ostream<_elem> &std::operator (std::basic_ostream<_elem> &,char)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\ostream(764): 或 'std::basic_ostream<_elem> &std::operator (std::basic_ostream<_elem> &,const 字符 *)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\ostream(811): 或 'std::basic_ostream<_elem> &std::operator (std::basic_ostream<_elem> &,char)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\ostream(937): 或 'std::basic_ostream<_elem> &std::operator (std::basic_ostream<_elem> &,const 签名字符 *)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\ostream(944): 或 'std::basic_ostream<_elem> &std::operator (std::basic_ostream<_elem> &,已签名字符)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\ostream(951): 或 'std::basic_ostream<_elem> &std::operator (std::basic_ostream<_elem> &,const 无符号字符 *）' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\ostream(958): 或 'std::basic_ostream<_elem> &std::operator (std::basic_ostream<_elem> ＆，无符号字符）' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\ostream(968): 或 'std::basic_ostream<_elem> &std::operator (std::basic_ostream<_elem> &&,_Ty)' 和 [ _Elem=char, _Traits=std::char_traits, _Ty=cs52::闪存盘 ] c:\program files\microsoft visual studio 10.0\vc\include\ostream(1085): 或 'std::basic_ostream<_elem> &std::operator (std::basic_ostream<_elem> &,const std::error_code &)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\ostream(186): 或 'std::basic_ostream<_elem> &std::basic_ostream<_elem>::operator 特征> &(_cdecl *)(std::basic_ostream<_elem> &))' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\ostream(192): 或 'std::basic_ostream<_elem> &std::basic_ostream<_elem>::operator 特征> &(_cdecl *)(std::basic_ios<_elem> &))' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\ostream(199): 或 'std::basic_ostream<_elem> &std::basic_ostream<_elem>::operator &std::basic_ostream<_elem>::operator &std::basic_ostream<_elem>::operator &std::basic_ostream<_elem>::operator &std::basic_ostream<_elem>::operator &std::basic_ostream<_elem>::operator &std::basic_ostream<_elem>::operator &std::basic_ostream<_elem>::operator &std::basic_ostream<_elem>特征>::operator _int64)' 和 [ _Elem=char, _Traits=std::char_traits ] c:\program files\microsoft visual studio 10.0\vc\include\ostream(386): 或 'std::basic_ostream<_elem> &std::basic_ostream<_elem>::operator &std::basic_ostream<_elem>::operator &std::basic_ostream<_elem>::operator &std::basic_ostream<_elem>::operator &std::basic_ostream<_elem>::operator &std::basic_ostream<_elem>::operator *)' 和 [ _Elem=char, _Traits=std::char_traits ] 在尝试匹配参数列表 '(std::ostream, cs52::FlashDrive)' c:\documents and settings\administrator\my 文件\视觉工作室 2010\projects\flashdriver\flashdriver\main.cpp(38)：错误 C2146：语法错误：缺少 ';'在标识符“-”之前 c:\documents 和设置\管理员\我的文档\visual studio 2010\projects\flashdriver\flashdriver\main.cpp(38)：错误 C2065：'–'：未声明的标识符 c:\documents and settings\administrator\my 文件\视觉工作室 2010\projects\flashdriver\flashdriver\main.cpp(38)：错误 C2146：语法错误：缺少';'在标识符 'drive1' FlashDrive.cpp 之前正在生成代码...

构建失败。

经过时间 00:00:01.82 ========== 构建：0 成功，1 失败，0 最新，0 跳过 ==========

【问题讨论】：

你试过什么？如果您没有为 FlashDrive 类指定任何操作员>>，错误消息有什么奇怪的？
第一条错误信息告诉你没有定义operator>>，这是真的。如果可能，请使用 SSCE (sscce.org) 逐步了解错误消息并提出更具体的问题

标签： c++ class exception namespaces operators

【解决方案1】：

你需要为class FlashDrive定义operator>>

friend std::istream& operator>>(std::istream& is, FlashDrive& fd)
{
  is >> my_StorageCapacity >> my_StorageUsed >> my_IsPluggedIn;
  return is;
}

类似的你可以定义operator<<

std::ostream& operator>>(std::ostream& os, const FlashDrive& fd)
{
  os << fd.getCapacity() << fd.getUsed() << fd.isPluggedIn();
  return os;
}

【讨论】：