书籍：C++ Primer Plus （第六版）（中文版）
工具：Dev-C++ 5.11
电脑信息：Intel® Xeon® CPU E5-2603 v3 @ 1.60GHz
系统类型：64位操作系统，基于X64的处理器 windows10 专业版
第12章 类和动态内存分配
12.1 动态内存和类
实例12.1
strngbad.h
cpp
#include <iostream>
#ifndef STRNGBAD_H_
#define STRNGBAD_H_
class StringBad
{
private:
char *str;
int len;
static int num_strings;
public:
StringBad(const char * s);
StringBad();
~StringBad();
friend std::ostream & operator<<(std::ostream & os, const StringBad & st);
};
#endifstrngbad.cpp
cpp
#include <cstring>
#include "strngbad.h"
using std::cout;
int StringBad::num_strings = 0;
StringBad::StringBad(const char * s)
{
len=std::strlen(s);
str=new char[len+1];
std::strcpy(str,s);
num_strings++;
cout<<num_strings<<": \""<<str<<"\" object created\n";
}
StringBad::StringBad()
{
len=4;
str=new char[4];
std::strcpy(str,"C++");
num_strings++;
cout<<num_strings<<": \""<<str<<"\" default object created\n";
}
StringBad::~StringBad()
{
cout<<"\""<<str<<"\" object deleted, \n";
--num_strings;
cout<<num_strings<<" left\n";
delete [] str;
}
std::ostream & operator<<(std::ostream & os,const StringBad & st)
{
os<<st.str;
return os;
}vegnews.cpp
cpp
#include <iostream>
using std::cout;
#include "strngbad.h"
void callme1(StringBad &);
void callme2(StringBad);
int main()
{
using std::endl;
{
cout<<"String an inner block.\n";
StringBad headline1("Celery stalks at Midnight");
StringBad headline2("Lettuce Prey");
StringBad sports("Spinach Leaves Bowl for dollars.");
cout<<"headline1: "<<headline1<<endl;
cout<<"headline2: "<<headline2<<endl;
cout<<"sports: "<<sports<<endl;
callme1(headline1);
cout<<"headline1: "<<headline1<<endl;
callme2(headline2);
cout<<"headline2: "<<headline2<<endl;
cout<<"Initialize one object to another:\n";
StringBad sailor = sports;
cout<<"sailor: "<<sailor<<endl;
cout<<"Assign one object to another:\n";
StringBad knot;
knot = headline1;
cout<<"knot: "<<knot<<endl;
cout<<"Exiting the block.\n";
}
cout<<"End of main()\n";
return 0;
}
void callme1(StringBad & rsb)
{
cout<<"String passed by refrence:\n";
cout<<" \""<<rsb<<"\"\n";
}
void callme2(StringBad sb)
{
cout<<"String passed by value:\n";
cout<<" \""<<sb<<"\"\n";
}编译运行结果：
cpp
String an inner block.
1: "Celery stalks at Midnight" object created
2: "Lettuce Prey" object created
3: "Spinach Leaves Bowl for dollars." object created
headline1: Celery stalks at Midnight
headline2: Lettuce Prey
sports: Spinach Leaves Bowl for dollars.
String passed by refrence:
"Celery stalks at Midnight"
headline1: Celery stalks at Midnight
String passed by value:
"Lettuce Prey"
"Lettuce Prey" object deleted,
2 left
headline2:
Initialize one object to another:
sailor: Spinach Leaves Bowl for dollars.
Assign one object to another:
3: "C++" default object created
knot: Celery stalks at Midnight
Exiting the block.
"Celery stalks at Midnight" object deleted,
2 left
"Spinach Leaves Bowl for dollars." object deleted,
1 left
"Spinach Leaves Bowl for dollars." object deleted,
0 left
--------------------------------
Process exited after 0.8916 seconds with return value 3221225477
请按任意键继续. . .12.2 改造后的新string类
实例12.2
string1.h
cpp
#ifndef STRING1_H_
#define STRING1_H_
#include <iostream>
using std::ostream;
using std::istream;
class String
{
private:
char * str;
int len;
static int num_strings;
static const int CINLIM = 80;
public:
String(const char * s);
String();
String(const String &);
~String();
int length() const {return len;}
String & operator=(const String &);
String & operator=(const char *);
char & operator[] (int i);
const char & operator[] (int i) const ;
friend bool operator<(const String &st,const String &st2);
friend bool operator>(const String &st1,const String &st2);
friend bool operator==(const String &st,const String &st2);
friend ostream & operator<<(ostream & os,const String & st);
friend istream & operator>>(istream & is,String & st);
static int Howmany();
};
#endifstring1.cpp
cpp
#include <cstring>
#include "string1.h"
using std::cin;
using std::cout;
int String::num_strings = 0;
int String::Howmany()
{
return num_strings;
}
String::String(const char * s)
{
len=std::strlen(s);
str=new char[len+1];
std::strcpy(str,s);
num_strings++;
}
String::String()
{
len=4;
str=new char[1];
str[0]='\0';
num_strings++;
}
String::String(const String & st)
{
num_strings++;
len=st.len;
str=new char [len+1];
std::strcpy(str,st.str);
}
String::~String()
{
--num_strings;
delete [] str;
}
String & String::operator=(const String & st)
{
if(this == &st)
{
return *this;
}
delete [] str;
len=st.len;
str=new char[len+1];
std::strcpy(str,st.str);
return *this;
}
String & String::operator=(const char * s)
{
delete [] str;
len=std::strlen(s);
str=new char[len+1];
std::strcpy(str,s);
return *this;
}
char & String::operator[](int i)
{
return str[i];
}
const char & String::operator[](int i) const
{
return str[i];
}
bool operator<(const String &st1,const String &st2)
{
return (std::strcmp(st1.str,st2.str)<0);
}
bool operator>(const String &st1,const String &st2)
{
return st2<st1;
}
bool operator==(const String &st1,const String &st2)
{
return (std::strcmp(st1.str,st2.str)==0);
}
ostream & operator<<(ostream &os,const String & st)
{
os<<st.str;
return os;
}
istream & operator>>(istream & is,String &st)
{
char temp[String::CINLIM];
is.get(temp,String::CINLIM);
if(is)
st=temp;
while(is && is.get() != '\n')
continue;
return is;
}sayings1.cpp
cpp
#include <iostream>
#include "string1.h"
const int ArSize =10;
const int MaxLen=81;
int main()
{
using std::cout;
using std::cin;
using std::endl;
String name;
cout<<"Hi,what's your name?\n>> ";
cin>>name;
cout<<name<<",please enter upto "<<ArSize
<<" short sayings <empty line to quit>:\n";
String sayings[ArSize];
char temp[MaxLen];
int i;
for(i=0;i<ArSize;i++)
{
cout<<i+1<<": ";
cin.get(temp,MaxLen);
while(cin && cin.get() != '\n')
continue;
if(!cin || temp[0] == '\0')
break;
else
sayings[i]=temp;
}
int total = i;
if(total>0)
{
cout<<"Here are your sayings:\n";
for(i=0;i<total;i++)
cout<<sayings[i][0]<<": "<<sayings[i]<<endl;
int shortest=0;
int first=0;
for(i=1;i<total;i++)
{
if(sayings[i].length()<sayings[shortest].length())
{
shortest =i;
}
if(sayings[i]<sayings[first])
first=i;
}
cout<<"shortest saying:\n"<<sayings[shortest]<<endl;
cout<<"First alphabetically:\n"<<sayings[first]<<endl;
cout<<"This program used: "<<String::Howmany()
<<"String objects.Bye!\n";
}
else
{
cout<<"No input! Bye.\n";
}
return 0;
}编译运行结果：
cpp
Hi,what's your name?
>> Misty guts
Misty guts,please enter upto 10 short sayings <empty line to quit>:
1: a fool and his money are soon parted
2: pnney wise,pound foolish
3: the love of money is the root of much evil
4: cut of sight,out of mind
5: absence makes the heart fonder
6: absinthe makes the hart grow fonder
7:
Here are your sayings:
a fool and his money are soon parted: a fool and his money are soon parted
pnney wise,pound foolish: pnney wise,pound foolish
the love of money is the root of much evil: the love of money is the root of much evil
cut of sight,out of mind: cut of sight,out of mind
absence makes the heart fonder: absence makes the heart fonder
absinthe makes the hart grow fonder: absinthe makes the hart grow fonder
shortest saying:
pnney wise,pound foolish
First alphabetically:
a fool and his money are soon parted
My favorite saying:
the love of money is the root of much evil
Bye.
--------------------------------
Process exited after 175.1 seconds with return value 0
请按任意键继续. . .12.3 在构造函数中使用new时应注意的事项
12.4 有关返回对象的说明
12.5 使用指向对象的指针
实例12.3
将实例12.2 的主文件修改为sayings2.cpp
cpp
#include <iostream>
#include <cstdlib>
#include <ctime>
#include "string1.h"
const int ArSize =10;
const int MaxLen=81;
int main()
{
using namespace std;
String name;
cout<<"Hi,what's your name?\n>> ";
cin>>name;
cout<<name<<",please enter upto "<<ArSize
<<" short sayings <empty line to quit>:\n";
String sayings[ArSize];
char temp[MaxLen];
int i;
for(i=0;i<ArSize;i++)
{
cout<<i+1<<": ";
cin.get(temp,MaxLen);
while(cin && cin.get() != '\n')
continue;
if(!cin || temp[0] == '\0')
break;
else
sayings[i]=temp;
}
int total = i;
if(total>0)
{
cout<<"Here are your sayings:\n";
for(i=0;i<total;i++)
cout<<sayings[i]<<": "<<sayings[i]<<endl;
String *shortest = &sayings[0];
String * first = &sayings[0];
for(i=1;i<total;i++)
{
if(sayings[i].length()<shortest->length())
shortest = &sayings[i];
if(sayings[i]<*first)
first=&sayings[i];
}
cout<<"shortest saying:\n"<<*shortest<<endl;
cout<<"First alphabetically:\n"<<*first<<endl;
srand(time(0));
int choice = rand()%total;
String *favorite = new String(sayings[choice]);
cout<<"My favorite saying:\n"<<*favorite<<endl;
delete favorite;
}
else
{
cout<<"Not much to say,eh?\n";
}
cout<<"Bye.\n";
return 0;
}编译运行结果：
cpp
Hi,what's your name?
>> Kirt Rood
Kirt Rood,please enter upto 10 short sayings <empty line to quit>:
1: a friend in need is a friend indeed
2: neither a borrower nor a lender be
3: a stitch in time saves nine
4: a niche in time saves stine
5: it takes a crook to catch a crook
6: cold hands,warm heart
7:
Here are your sayings:
a friend in need is a friend indeed: a friend in need is a friend indeed
neither a borrower nor a lender be: neither a borrower nor a lender be
a stitch in time saves nine: a stitch in time saves nine
a niche in time saves stine: a niche in time saves stine
it takes a crook to catch a crook: it takes a crook to catch a crook
cold hands,warm heart: cold hands,warm heart
shortest saying:
cold hands,warm heart
First alphabetically:
a friend in need is a friend indeed
My favorite saying:
a friend in need is a friend indeed
Bye.
--------------------------------
Process exited after 124.1 seconds with return value 0
请按任意键继续. . .实例12.4
placenew1.cpp
cpp
#include <iostream>
#include <string>
#include <new>
using namespace std;
const int BUF = 512;
class JustTesting
{
private:
string words;
int number;
public:
JustTesting(const string & s ="Just Testing",int n=0)
{
words =s;
number=n;
cout<<words<<" constructed\n";
}
~JustTesting()
{
cout<<words<<" destroyed\n";
}
void show() const
{
cout<<words<<", "<<number<<endl;
}
};
int main()
{
char * buffer = new char[BUF];
JustTesting *pc1,*pc2;
pc1=new (buffer) JustTesting;
pc2=new JustTesting("Heap1",20);
cout<<"Memory block addresses:\n"<<"buffer: "
<<(void *)buffer<<" heap: "<<pc2<<endl;
cout<<"Memory contents:\n";
cout<<pc1<<": ";
pc1->show();
cout<<pc2<<": ";
pc2->show();
JustTesting *pc3,*pc4;
pc3=new (buffer) JustTesting("Bad Idea",6);
pc4=new JustTesting("Heap2",10);
cout<<"Memory contents:\n";
cout<<pc3<<": ";
pc3->show();
cout<<pc4<<": ";
pc4->show();
delete pc2;
delete pc4;
delete [] buffer;
cout<<"Done\n";
return 0;
}编译运行结果：
cpp
Just Testing constructed
Heap1 constructed
Memory block addresses:
buffer: 0xb25940 heap: 0xb21900
Memory contents:
0xb25940: Just Testing, 0
0xb21900: Heap1, 20
Bad Idea constructed
Heap2 constructed
Memory contents:
0xb25940: Bad Idea, 6
0xb25bb0: Heap2, 10
Heap1 destroyed
Heap2 destroyed
Done
--------------------------------
Process exited after 0.2065 seconds with return value 0
请按任意键继续. . .实例12.5
placenew2.cpp
cpp
#include <iostream>
#include <string>
#include <new>
using namespace std;
const int BUF = 512;
class JustTesting
{
private:
string words;
int number;
public:
JustTesting(const string & s ="Just Testing",int n=0)
{
words =s;
number=n;
cout<<words<<" constructed\n";
}
~JustTesting()
{
cout<<words<<" destroyed\n";
}
void show() const
{
cout<<words<<", "<<number<<endl;
}
};
int main()
{
char * buffer = new char[BUF];
JustTesting *pc1,*pc2;
pc1=new (buffer) JustTesting;
pc2=new JustTesting("Heap1",20);
cout<<"Memory block addresses:\n"<<"buffer: "
<<(void *)buffer<<" heap: "<<pc2<<endl;
cout<<"Memory contents:\n";
cout<<pc1<<": ";
pc1->show();
cout<<pc2<<": ";
pc2->show();
JustTesting *pc3,*pc4;
pc3=new (buffer + sizeof(JustTesting)) JustTesting("Better Idea",6);
pc4=new JustTesting("Heap2",10);
cout<<"Memory contents:\n";
cout<<pc3<<": ";
pc3->show();
cout<<pc4<<": ";
pc4->show();
delete pc2;
delete pc4;
pc3->~JustTesting();
pc1->~JustTesting();
delete [] buffer;
cout<<"Done\n";
return 0;
}编译运行结果：
cpp
Just Testing constructed
Heap1 constructed
Memory block addresses:
buffer: 0x1d5940 heap: 0x1d1900
Memory contents:
0x1d5940: Just Testing, 0
0x1d1900: Heap1, 20
Better Idea constructed
Heap2 constructed
Memory contents:
0x1d5950: Better Idea, 6
0x1d5bb0: Heap2, 10
Heap1 destroyed
Heap2 destroyed
Better Idea destroyed
Just Testing destroyed
Done
--------------------------------
Process exited after 0.2174 seconds with return value 0
请按任意键继续. . .