C++ Primer Plus(6th edition) 第12章程式設計練習題
1.對於下面的類宣告 class Cow { char name[20]; char * hobby; double weight; public: Cow(); Cow(const char*nm, const char * ho, double wt); Cow(const Cow &c); ~Cow(); Cow & operator=(const Cow &c); void ShowCow() const; //display all cow data };給這個類提供實現，並編寫一個使用所有成員函式的小程式。
//cow.h #ifndef COW_H_ #define COW_H_ #include<iostream> #include<string> #include<stdio.h> using namespace std; class Cow { private: char name[20]; char *hobby; double weight; public: Cow(); Cow(const char *nm, const char *ho, double wt); Cow(const Cow &c); ~Cow(); Cow &operator=(const Cow &c); void ShowCow()const; }; #endif
//cow.cpp #include"cow.h" Cow::Cow() { name[0] = '\0'; hobby = new char[1]; hobby[0] = '\0'; weight = 0; } Cow::Cow(const char *nm, const char *ho, double wt) { strcpy_s(name, 20, nm); hobby = new char[strlen(ho) + 1]; strcpy_s(hobby, strlen(ho) + 1, ho); weight = wt; } Cow::Cow(const Cow &c) { strcpy_s(name, 20, c.name); hobby = new char[strlen(c.hobby) + 1]; strcpy_s(hobby, strlen(c.hobby) + 1, c.hobby); weight = c.weight; } Cow::~Cow() { delete[]hobby; } Cow &Cow::operator=(const Cow &c) { if (this == &c) return *this; delete[]hobby; hobby = new char[strlen(c.hobby) + 1]; strcpy_s(hobby, strlen(c.hobby) + 1, c.hobby); strcpy_s(name, 20, c.name); weight = c.weight; return *this; } void Cow::ShowCow()const { cout << "Cow name: " << name << endl; cout << "Cow hobby: " << hobby << endl; cout << "Cow weight: " << weight << endl; }
//main.cpp
#include"cow.h"
int main()
{
Cow co1;
Cow co2("cow1", "sport", 123);
Cow co3(co2);
co1 = co2;
co1.ShowCow();
co2.ShowCow();
co3.ShowCow();
system("pause");
return 0;
}
*題目核心：
（1）strcpy_s函式的使用：
該函式是VS2005之後的VS提供的，並非C標準函式
原型：strcpy_s( char *dst, size_t num, const char *src ）
功能：同strcpy()函式功能相同，不同之處在於引數中多了個size_t型別的引數，該引數為字串dst的長度，當存在快取區溢位的問題時（即src的長度大於dst的長度），strcpy_s()會丟擲異常；而strcpy()結果則未定，因為它錯誤地改變了程式中其他部分的記憶體的資料，可能不會丟擲異常但導致程式資料錯誤，也可能由於非法記憶體訪問丟擲異常。
Cow::Cow(const Cow &c)
{
strcpy_s(name, 20, c.name);
hobby = new char[strlen(c.hobby) + 1];
strcpy_s(hobby, strlen(c.hobby) + 1, c.hobby);
weight = c.weight;
}(2) 過載賦值運算子：
Cow &Cow::operator=(const Cow &c)
{
if (this == &c) //如果物件賦值給自身
return *this;
delete[]hobby; //釋放舊字串
hobby = new char[strlen(c.hobby) + 1]; //為新字串分配記憶體
strcpy_s(hobby, strlen(c.hobby) + 1, c.hobby); //複製字串
strcpy_s(name, 20, c.name);
weight = c.weight;
return *this; //返回一個指向呼叫物件的引用
}2.通過完成下面的工作來改進String類宣告（即將String1.h升級為String2.h）。 a。對+運算子進行過載，使之可將兩個字串合併成1個。 b。提供一個Stringlow()成員函式，將字串中所有的字母字元轉換為小寫（別忘了cctype系列字元函式）。 c。提供String()成員函式，將字串中所有字母字元轉換成大寫。 d。提供一個這樣的成員函式，它接受一個char引數，返回該字元在字串中出現的字數。 使用下面的程式來測試您的工作： //pe12_2.cpp #include<iostream> using namespace std; #include"string2.h" int main() { String s1(" and I am a C++ student."); String s2 = "Please enter your name: "; String s3; cout << s2; //overload <<operator cin >> s3; //overload >>operator s2 = "My name is " + s3; //overload = , + operators cout << s2 << ".\n"; s2 = s2 + s1; s2.stringup(); //converts string to uppercase cout << "The string\n" << s2 << "\ncontains " << s2.has('A') << " 'A' characters in it.\n"; s1 = "red"; //String (const char *), //then String & operator= (const String&) String rgb[3] = { String(s1), String("green"), String("blue")}; cout << "Enter the name of a primary color for mixing light: "; String ans; bool success = false; while (cin >> ans) { ans.stringlow(); //converts string to lowercase for (int i = 0; i < 3; i++) { if (ans == rgb[i]) //overload == operator { cout << "That's right!\n"; success = true; break; } } if (success) break; else cout << "Try again!\n"; } cout << "Bye\n"; return ; } 輸出應與下面相似： Please enter your name: Fretts Farbo My name is Fretta Farbo. The strign MY NAME ISFRETTA FARBO AND I AM A C++ STUDENT. contains 6 'A' characters in it. Enter the name of a primary color for mixing light: yellow Try again! BLUE Tha's right! Bye
//String.h
#ifndef STRING_H_
#define STRING_H_
#include <iostream>
#include <stdio.h>
#include <cstring>
#include <string.h>
using namespace std;
class String
{
public:
String(const char *s);
String();
String(const String &);
~String();
int length()const { return len; }
String &operator=(const String &st); //過載賦值運算子
String &operator=(const char *);
void stringlow();
void stringup();
int has(const char ch);
friend String operator+(const char *s, const String &st);
friend bool operator<(const String &st1, const String &st2);
friend bool operator>(const String &st1, const String &st2);
friend bool operator==(const String &st1, const String &st2);
friend String operator+(const String &st1, const String &st2);
friend ostream &operator<<(ostream &os, const String &st);
friend istream &operator>>(istream &is, String &st);
static int HowMany();
private:
char *str;
int len;
static int num_strings;
static const int CINLIM = 80;
};
#endif//String.cpp
#include "String.h"
int String::num_strings = 0;
int String::HowMany()
{
return num_strings;
}
String::String(const char *s)
{
len = strlen(s);
str = new char[len + 1];
strcpy_s(str, len + 1, 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];
strcpy_s(str, len + 1, 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];
strcpy_s(str, len + 1, st.str);
return *this;
}
String &String::operator=(const char *s)
{
delete[]str;
len = strlen(s);
str = new char[len + 1];
strcpy_s(str, len + 1, s);
return *this;
}
void String::stringlow()
{
for (int i = 0; i < len; i++)
{
if (isupper(str[i]))
str[i] = tolower(str[i]);
}
}
void String::stringup()
{
for (int i = 0; i < len; i++)
{
if (islower(str[i]))
str[i] = toupper(str[i]);
}
}
int String::has(const char ch)
{
int counts = 0;
for (int i = 0; i < len; i++)
{
if (str[i] == ch)
counts++;
}
return counts;
}
bool operator<(const String &st1, const String &st2)
{
return (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 (strcmp(st1.str, st2.str) == 0);
}
String operator+(const char *s, const String &st) //友元：常量字串+物件
{
int lens = strlen(s) + st.len;
char *ps = new char[lens + 1];
strcpy_s(ps, lens + 1, s);
strcat_s(ps, lens + 1, st.str);
return String(ps);
}
String operator+(const String &st1, const String &st2) //友元：物件+物件
{
int lens = st1.len + st2.len;
char *ps = new char[lens + 1];
strcpy_s(ps, lens + 1, st1.str);
strcat_s(ps, lens + 1, st2.str);
return String(ps);
}
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;
}//main.cpp
#include"String.h"
int main()
{
String s1(" and I am a C++ student.");
String s2 = "Please enter your name: ";
String s3;
cout << s2; //過載<<運算子
cin >> s3; //過載>>運算子
s2 = "My name is " + s3; //過載+,=運算子
cout << s2 << ".\n";
s2 = s2 + s1;
s2.stringup(); //將字串轉化為大寫
cout << "The string\n" << s2 << "\ncontains " << s2.has('A')
<< " 'A' characters in it.\n";
s1 = "red"; //呼叫String(const char *),
//然後呼叫 String & operator=(const String &)
String rgb[3] = { String(s1), String("green"), String("blue") };
cout << "Enter the name of a primary color for mixing light: ";
String ans;
bool success = false;
while (cin >> ans)
{
ans.stringlow(); //將字串轉換為小寫
for (int i = 0; i < 3; i++)
{
if (ans == rgb[i]) //過載==運算子
{
cout << "That's right!\n";
success = true;
break;
}
}
if (success)
break;
else
cout << "Try again!\n";
}
cout << "Bye\n";
system("pause");
return 0;
}
執行結果：
Please enter your name: Fretta Farbo My name is Fretta Farbo. The string MY NAME IS FRETTA FARBO AND I AM A C++ STUDENT. contains 6 'A' characters in it. Enter the name of a primary color for mixing light: yellow Try again! BLUE That's right! Bye
*題目核心知識點：
(1) 過載賦值運算子
String &operator=(const String &st); //過載賦值運算子
String &operator=(const char *);(2) 友元過載+運算子
friend String operator+(const char *s, const String &st);
friend String operator+(const String &st1, const String &st2);完整的程式設計練習程式碼可在如下連結下載：