第8周 项目4 String类的构造

问题及代码：

/*。*Copyright(c)2014,烟台大学计算机学院*All right reserved,*文件名：test.cpp*作者：liu_feng_zi_*完成日期：2015年5月10日*版本号：v1.0*问题描述：请构造String类的加、减运算。其中，s1 + s2将两个字符串的连接起来；s1 - s2是将s1的尾部空格和s2的前导空格去除后的连接。*输入描述：*程序输出：*/#include <iostream>#include <Cstring>using namespace std;class String{public:    String( );    String(const char *s);    String(String &str);    ~String();    void display( );    friend String operator + (String &s1,String &s2 );    friend String operator - (String &s1,String &s2 );private:    char *p;    int len;};String::String(){    len = 0;    p = NULL;}String::String(const char *s){    len = strlen(s);    p = new char[len+1];    strcpy(p,s);}String::String(String &str){    len = str.len;    if(p!=NULL) delete []p;    p = new char[len+1];    strcpy(p,str.p);}String::~String(){    if(!p) delete []p;}void String::display( ){    cout<<p<<endl;}String operator + (String &s1, String &s2 ){    String s;    s.len = s1.len+s2.len;    s.p = new char[s.len+1];    strcpy(s.p,s1.p);    strcat(s.p,s2.p);    return s;}String operator - (String &s1, String &s2 ){    String s;    char *c1=new char[s1.len+1];    strcpy(c1,s1.p);    int i=s1.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;}int main( ){    String string1(" Hello  "), string2(" World ");    string1.display();    string2.display();    String string3;    string3 = string1 + string2;    string3.display();    string3 = string1 - string2;    string3.display();    return 0;}

运行结果：