作为我们下周的考试复习包的一部分,我们被要求理解超载操作员的指示 - 我发现很难得到的东西,导师拒绝给我们任何一个例子,并要求他独立研究。
显然我们将在决赛中遇到其中一个问题,我想确保我正确理解这个练习。
这种做法涉及运算符重载的问题。我们被要求实施<<和>>。 我们要:
使用您一直在使用的FlashDrive类,升级该类 运算符<<和运算符>>适用于指针(即, FlashDrive *)。你需要重新加载这些运算符,添加 功能:
朋友std :: ostream& operator<<(std :: ostream& outs,const FlashDrive * drive);
朋友std :: istream&运算符>>(std :: istream& ins,FlashDrive *& drive);
提示:要非常小心地测试NULL
注意:这些想法将成为下周工作的一部分!
我正在使用的代码是
FlashDrive.h
#ifndef FLASHDRIVE_H
#define FLASHDRIVE_H
class FlashDrive {
public:
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;
int my_StorageUsed;
bool my_IsPluggedIn;
}
#endif
FlashDriver.cpp ---驱动程序类
#include <iostream>
#include "FlashDrive.h"
using namespace cs52;
void main( )
{
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...
}
// work with the new stuff added for Unit 16!!!
cs52::FlashDrive * drive3 = NULL;
// careful...
cout << drive3 << endl;
drive3 = &drive2;
cout << drive3 << endl;
drive3 = new FlashDrive();
cin >> drive3;
cout << drive3 << endl;
delete( drive3 );
}
我想看看一个有效的实现类是什么样的,所以我可以对它进行逆向工程并将其用作学习源。我发现其中一些指针非常具有挑战性
我已编码的实现类位于
之下FlashDrive.cpp
#include "FlashDrive.h"
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 );
}
修改::::::
我更新了.h和.cpp 但我仍然无法正确添加&lt;&lt;和&gt;&gt;运营商:-( 任何想法??
·H
#ifndef FLASHDRIVE_H
#define FLASHDRIVE_H
namespace cs52
{
class FlashDrive {
friend FlashDrive operator+ (FlashDrive used1 , FlashDrive used2);
friend FlashDrive operator- (FlashDrive used3, FlashDrive used4 );
public:
friend std::ostream& operator <<( std::ostream& outs, const FlashDrive * drive );
friend std::istream& operator >>( std::istream& ins, FlashDrive * & drive );
FlashDrive& FlashDrive::operator=(int);
FlashDrive::FlashDrive(int);
FlashDrive(const std::string &name): name_(name){
}
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;
std::string name_;
int my_StorageUsed;
bool my_IsPluggedIn;
}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
的.cpp
#include <cstdlib>
#include <iostream>
#include "FlashDrive.h"
using namespace cs52;
using namespace std;
std::ostream& operator <<(std::ostream& outs, const FlashDrive * drive )
{
outs << drive->name_;
return outs;
}
std::istream& operator >>( std::istream& ins, FlashDrive * & drive )
{
ins >> drive->name_;
return ins;
}
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 );
}
答案 0 :(得分:4)
我想看看工作实现类的外观 像
你走了:
#include <iostream>
class Llama
{
private:
std::string name_;
public:
Llama(const std::string &name): name_(name)
{}
friend std::ostream &operator<<(std::ostream &o, const Llama *);
};
std::ostream &operator<<(std::ostream &o, const Llama *llama)
{
o << llama->name_;
return o; /* this is important, because it allows chaining */
}
int main(int, char **)
{
Llama *llama = new Llama("Meh");
std::cout << llama << " is the name of my llama" << std::endl;
return (0);
}
我的意思是“链接”:
std::cout << llama
将首先执行。这将返回std::ostream
引用:在这种情况下,此引用本身为std::cout
。std::cout << llama
“替换”std::cout
。std::cout << " is the ..."
将被执行。然后是std::cout << std::endl
。这就是为什么返回std::ostream
的引用很重要。