第八周项目4--String类的构造

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/**Copyright (c) 2014, 烟台大学计算机学院*All rights reserved.*文件名称：test.cpp*作者：于凯*完成日期：2015年 5月 9 日*版本号：v1.0*/#include <iostream>#include <cstring>using namespace std;class String{public:    String();    String(const char *);    String operator+(const String &);    String operator-(const String &);    void display();private:    char *p;    int len;};String::String(){    p=NULL;    len=0;}String::String(const char *a){    len=strlen(a);    p=new char[len+1];    strcpy(p,a);}String String::operator+(const String &s2){    String s;    s.len=this->len+s2.len;    s.p=new char[s.len+1];    strcpy(s.p,this->p);    strcat(s.p,s2.p);    return s;}String String::operator-(const String &s2){    String s;    char *c1=new char[this->len+1];    strcpy(c1,this->p);    int i=this->len-1;    while(i>=0&&c1[i]==' ') --i;    c1[i+1]='\0';    char *c2=new char[s2.len+1];    strcpy(c2,s2.p);    i=0;    while(i<s2.len&&c2[i]==' ') ++i;    int j=0;    while(i<s2.len&&c2[i]!='\0')    {        c2[j]=c2[i];        ++i;        ++j;    }    c2[j]='\0';    s.len = strlen(c1)+strlen(c2);    s.p = new char[s.len+1];    strcpy(s.p,c1);    strcat(s.p,c2);    delete c1;    delete c2;    return s;}void String::display(){    cout<<p<<endl;}int main(){    String s1("dong liang"),s2(" shi zhu zi"),s3;    s3=s1+s2;    cout<<"s1+s2=";    s3.display();    s3=s1-s2;    cout<<"s1-s2=";    s3.display();    return 0;}

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