请教为何出现段错误

[tcbsyao]

1 #include <iostream>
2 using namespace std;
3 #include <string>
4
5 class String
6 {
7 char* x;
8 public:
9 String(char* x):x(0){}
10 String(const String& s){}
11 friend String operator+(const String& s2,const String& s3);
12 friend ostream& operator<<(ostream& o,const String& s1);
13
14 };
15 String operator+(const String& s2,const String& s3)
16 {
17 char* x=strcat(s2.x,s3.x);
18 return String(x);
19 }
20 ostream& operator<<(ostream& o,const String& s)
21 {
22 o<<s.x;
23 return o;
24 }
25
26 int main()
27 {
28 String string1("abc"),string2("efg"),string3("hij");
29 string1=string2+string3;
30 cout<<string1;
31 }

[ttkk_2007]

String(char* x):x(0){} //x(0)??
char* x=strcat(s2.x,s3.x); //s2.x不够大，不能存储两个字符串的和
好多错误

[hoohag]

把你的String 的类的构造函数改一下

#include  <iostream>
using namespace std;
#include  <string>
 
class String
{

	public:
	char* m_x;
	String(char* x){
		m_x = new char[strlen(x)];
		strcpy(m_x, x);
	}
	String(const String& s){}
	friend String operator+(const String& s2,const String& s3);
	friend ostream& operator <<(ostream& o,const String& s1);
};
String operator+(const String& s2,const String& s3)
{
	char* m_x = strcat(s2.m_x,s3.m_x);
	return String(m_x);
}
ostream& operator <<(ostream& o,const String& s)
{
	o <<s.m_x;
	return o;
}

int main()
{
	String string1("abc"), string2("efg"), string3("hij");
	string1 = string2 + string3;
	cout << string1;
	system("Pause");
} 

[ttkk_2007]

2楼明显不对，加完了之后，连string2都变了
m_x = new char[strlen(x)]; //m_x = new char[strlen(ｘ) +１];

[帅得不敢出门]

引用 2楼 m_x = new char[strlen(x)+1];

还有楼主没有=的操作符重载

[ttkk_2007]

class String
{
 char* m_x;
    public:
   
    String(char* x){
        m_x = new char[strlen(x) + 1];
        strcpy(m_x, x);
    }
	~String(){
		delete m_x;
		m_x = NULL;
	}
    String(const String& s){
		m_x = new char[strlen(s.m_x) + 1];
		strcpy(m_x, s.m_x);
	}
	String & operator = (const String &s){
		if(this == &s)
			return *this;
		delete m_x;
		m_x = new char[strlen(s.m_x) + 1];
		strcpy(m_x, s.m_x);
		return *this;
	}
    friend String operator+(const String& s2,const String& s3);
    friend ostream& operator <<(ostream& o,const String& s1);
};
String operator+(const String& s2,const String& s3)
{
	char *p = new char[strlen(s2.m_x) + strlen(s3.m_x) + 1] ;
	strcpy(p, s2.m_x);
	strcat(p, s3.m_x);
	String temp(p);
	delete p;
    return temp;
}
ostream& operator <<(ostream& o,const String& s)
{
    o <<s.m_x;
    return o;
}

int main()
{
    String string1("abc"), string2("zhu"), string3("loiu");
    string1 = string2 + string3;

    cout << string1 << endl;

} 

[hoohag]

[Quote=引用 3 楼 ttkk_2007 的回复:]
2楼明显不对，加完了之后，连string2都变了
m_x = new char[strlen(x)]; //m_x = new char[strlen(ｘ) +１];
[/Quote]

呵呵, 忘记加1了. 对于上面的回复我只是为了说明构造函数, 对其他函数的功能, 没有仔细检查. 所以造成string2
的问题.