cpp题目

一、简答题。(共4题,共20分,每题5分)

1. void GetMemory(char *p) { p = (char *)malloc(100); } void Test(void) { char *str = NULL; GetMemory(str);     strcpy(str, "hello world"); printf(str); } 请问运行Test函数会有什么样的结果？ 最佳答案是:程序崩溃。因为GetMemory并不能传递动态内存， Test函数中的str一直都是 NULL。strcpy(str, "hello world");将使程序崩溃。     2. char *GetMemory(void) {   char p[] = "hello world"; return p; } void Test(void) { char *str = NULL; str = GetMemory();    printf(str); } 请问运行Test函数会有什么样的结果？ 有可能会导致程序崩溃，因为函数GetMemory 返回的是局部空间的地址。 3. void GetMemory(char **p, int num) { *p = (char *)malloc(num); } void Test(void) { char *str = NULL; GetMemory(&str, 100); strcpy(str, "hello");   printf(str);    } 请问运行Test函数会有什么样的结果？   最佳答案是:能够输出hello,内存泄漏     4. void Test(void) { char *str = (char *) malloc(100);     strcpy(str, "hello");     free(str);          if(str != NULL)     {       strcpy(str, “world”); printf(str); } } 请问运行Test函数会有什么样的结果? 最佳答案是:篡改动态内存区的内容，后果难以预料，非常危险。因为free(str);之后，str成为野指针， if(str != NULL)语句不起作用。

 

二、编程题（共10分）   . 已知strcpy函数的原型是 char *strcpy(char *strDest, const char *strSrc); 其中strDest是目的字符串，strSrc是源字符串。 （1）不调用C++/C的字符串库函数，请编写函数 strcpy （2）strcpy能把strSrc的内容复制到strDest，为什么还要char * 类型的返回值？   最佳答案是: char * strcpy(char * strDest,const char * strSrc) {   char * strDestCopy=strDest; //[3]   if((strDest==NULL)||(strSrc==NULL)) //[1]     throw "Invalid argument(s)"; //[2]   while((*strDest++=*strSrc++)!='\0'); //[4]   return strDestCopy; } 返回strDest的原始值使函数能够支持链式表达式，增加了函数的“附加值”。同样功能的函数，如果能合理地提高的可用性，自然就更加理想 三、使用继承实现以下几个类 Person(5分) Student(10分) GarduateStudent(15分) #include <iostream> #include <cstring> using namespace std;   class Person { public:     Person()     {         next_id++;         name = new char[1];         strcpy(name, "");         id = next_id;     }     Person(char* _name)     {         next_id++;         name = new char[strlen(_name)+1];         strcpy(name, _name);         id = next_id;     }         Person(const Person& _p)     {         next_id++;         name = new char[strlen(_p.name)+1];         strcpy(name, _p.name);         id = next_id;     }         const Person& operator=(const Person& p)     {         if (this != &p)         {             delete []name;             name = new char[strlen(p.name)+1];             strcpy(name, p.name);             id = p.id;         }                 return *this;     }         ~Person()     {         delete [] name;         name = NULL;     }         void print()     {         cout<<"名字为:"<<name<<"id:"<<id<<endl;     }     private:     char* name;     int id;     static int next_id; };   int Person::next_id = 0;   class Student:public Person { public:     Student()     {         label = new char[1];         strcpy(label, "");         grade = 0;     }     Student(char* _name,char* _label,int _grade):Person(_name)     {         label = new char[strlen(_label)+1];         strcpy(label, _label);         grade = _grade;     }         Student(const Student& s):Person(s)     {         label = new char[strlen(s.label)+1];         strcpy(label, s.label);         grade = s.grade;     }             const Student& operator=(const Student& s)     {         if (this != &s)         {             Person::operator=(s);             delete [] label;             label = new char[strlen(s.label)+1];             strcpy(label, s.label);             grade = s.grade;         }         return *this;     }         ~Student()     {         delete [] label;         label = NULL;     }         void print()     {         Person::print();         cout<<"label:"<<label<<"grade:"<<grade<<endl;     }     private:     char* label;     int grade; };   class GraduateStudent:public Student { public:     GraduateStudent()     {         message = new char[1];         strcpy(message, "");         salary = 1000;     }         GraduateStudent(char* _name,char* _label,int _grade,char* _message,int _salary):Student(_name,_label,_grade)     {         message = new char[strlen(_message)+1];         strcpy(message, _message);         salary = _salary;     }         GraduateStudent(const GraduateStudent& g):Student(g)     {         message = new char[strlen(g.message)+1];         strcpy(message, g.message);         salary = g.salary;     }         const GraduateStudent& operator=(const GraduateStudent& g)     {         if (this != &g)         {             Student::operator=(g);             delete [] message;             message = new char[strlen(g.message)+1];             strcpy(message, g.message);             salary = g.salary;         }                 return *this;     }         ~GraduateStudent()     {         delete [] message;         message = NULL;     }         void print()     {         Student::print();         cout<<"message:"<<message<<"salary:"<<salary<<endl;     }     private:     char* message;//盛放毕业信息     int salary; };   int main() {     Person p;     Person p1("zhangsan");     Person p2(p1);     p2.print();     p2 = p;     p1.print();     cout<<"test student"<<endl;     Student s;     Student s1("lisi","student1",100);     Student s2(s1);     s2.print();     s2=s;     s1.print();     cout<<"test graduatestudent"<<endl;     GraduateStudent gs;     GraduateStudent gs1("wangwu","student2",99,"biyesheng",10000);     GraduateStudent gs2(gs1);     gs2.print();     gs2 = gs;     gs1.print();     return 0; }   四、实现以下的String类   class  String { friend bool operator==(const String&, const String&); friend String operator+(const String&, const String&); friend bool operator<(const String&, const String&); public: String(); String(char*); String(const String&); const String& operator=(const String&); const String& operator+=(const String&); const char& at(int) const; // 如果越界要抛出异常 char& at(int); // 如果越界要抛出异常 const char& operator[](int)const; char&operator[](int); int length(); private: char* rep; // 存放字符串 int len; // 字符串的长度 };   最佳答案是: #include <iostream> #include <cstring> using namespace std;   int     strcmp1(const char * p, const char * q) {     while (*p==*q && *p!='\0' && *q!='\0')     {         p++;         q++;     }         if (*p==*q)     {         return 0;     }     return *p-*q; }   char* strcat1(char * p, const char * q) {     if (p==NULL || q==NULL)     {         throw "invalid arguments";     }     char* pt = p;     while (*p!='\0')     {         p++;     }     while (*q != '\0')     {         *p++ = *q++;     }     *p = '\0';         return pt; }   class String { public:     String()     {         rep = new char[1];         strcpy(rep, "");         size = 0;     }     String(char* _rep)     {         size = (int)strlen(_rep);         rep = new char[size+1];         strcpy(rep, _rep);     }         String(const String& s)     {         size = s.size;         rep = new char[size+1];         strcpy(rep, s.rep);     }         const String& operator=(const String& s)     {         if (this!=&s)         {             delete [] rep;             rep = new char[s.size+1];             strcpy(rep, s.rep);             size = s.size;         }                 return *this;     }         const char& operator[](int index)const     {         return rep[index];     }         char& operator[](int index)     {         return rep[index];     }         const char& at(int index) const     {         if(index >= size||index<0)             throw "越界";         return rep[index];     }         char& at(int index)     {         if(index >= size||index<0)             throw "越界";         return rep[index];     }         const String& operator+=(const String& s)     {         *this = *this + s;         return *this;     }         friend ostream& operator<<(ostream& out,const String& s)     {         out<<s.size<<endl;         out<<s.rep<<endl;         return out;     }     //cin>>p     //     friend bool operator<(const String& s1, const String& s2)     {         if(strcmp1(s1.rep,s2.rep) == -1)             return true;         return false;     }     friend istream& operator>>(istream& in,String& s)     {//gets(a);         cout<<"请输入您所输入的字符串的长度"<<endl;         in>>s.size;         delete [] s.rep;         s.rep = new char[s.size+1];         cout<<"请输入您所输入的字符串"<<endl;         in>>s.rep;         return in;     }         friend bool operator==(const String& s1,const String& s2)     {                 return !strcmp1(s1.rep, s2.rep);     }     //"abc"  "edf"         friend const String operator+(const String& s1,const String& s2)     {//size rep         String tmp(s1);//rep         //空间         tmp.size+=s2.size;         char* temp = tmp.rep;         //delete []tmp.rep;         tmp.rep = new char[tmp.size+1];         strcat1(tmp.rep, temp);         strcat1(tmp.rep, s2.rep);         delete [] temp;         return tmp;     }         int length()     {         return size;     }          ~String()     {         delete [] rep;         rep = NULL;     } private:     char* rep;     int size;//字符串的长度 }; int main() {     return 0; }