急!一个C++问题!希望大家能帮个忙!谢谢

[zcl198715]

//此程序是建立链表相关的操作
#include <iostream>
#include <string>
using namespace std;//申明结构

struct Elephant
{
string name;
Elephant* next;
};

void print_elephants( const Elephant* ptr );
Elephant* get_elephants();
void free_list( const Elephant* ptr );

int main()
{
Elephant* start;
start = get_elephants();
print_elephants( start );//由于start是指针类型,作为此函数的参数,会在此函数的作用下,start所指向的内存地址会改变,当此函数返回时,start已经为0
free_list( start ); //因此,当再调free_list(start)时,按理说应该不有任何作用了,但此函数还是被调用了!也就是说此时start还是start=get_elephants(),这是为什么啊?
return 0;
}

Elephant* get_elephants()//创建链表
{
Elephant *current,*first;
int response;
current =first=new Elephant;
cout << "\nNAME: ";
cin >> current -> name;
cout << "\nAdd another? (1 == yes, 0 == no): ";
cin >> response;
while ( response == 1 )
{
current = current -> next = new Elephant;
cout << "\nNAME: ";
cin >> current -> name;
cout << "\nAdd another? (1 == yes, 0 == no): ";
cin >> response;
}
current -> next = 0;
return first;
}


void print_elephants( const Elephant* ptr )//打印
{
int count = 1;
cout << "\n\n\n";
while ( ptr != 0 ) {
cout << "Elephant number " << count++
<< " is " << ptr -> name << '\n';
ptr = ptr -> next;
}
}

void free_list( const Elephant* ptr )//释放
{
const Elephant* temp_ptr;
while ( ptr != 0 )
{
cout<<"1111111111111111"<<endl;
temp_ptr = ptr -> next;
delete ptr;
ptr = temp_ptr;
}
}


希望高手们能帮个忙,小弟我不胜感谢!

[baihacker]

print_elephants( start );//由于start是指针类型,作为此函数的参数,会在此函数的作用下,start所指向的内存地址会改变,当此函数返回时,start已经为0

在函数内的那个是指针的一个副本
相当于

void print_elephants( const Elephant* ptr )//打印

在进入函数的时候 定义一个指针 ptr , 值为start的值, 也就是说指向同一个地方
当 ptr指向零的时候start还是指向那里

[ryfdizuo]

程序没有错误啊，可以的啊。是不是编译器的问题，我是vs2005

[ryfdizuo]

//编译，运行没有问题；
#include  <iostream> 
#include  <string> 
using namespace std;//申明结构 

struct Elephant 
{ 
	string name; 
	Elephant* next; 
}; 

void      print_elephants( const Elephant* ptr ); 
Elephant* get_elephants(); 
void      free_list( const Elephant* ptr ); 

int main()  
{ 
	Elephant* start; 
	start = get_elephants(); 
	print_elephants( start );
	free_list( start ); 

	return 0; 
} 

Elephant* get_elephants()//创建链表 
{ 
	Elephant *current,*first; 
	int response; 
	current =first=new Elephant; 
	cout  << "\nNAME: "; 
	cin >>  current ->name; 
	cout  << "\nAdd another? (1 == yes, 0 == no): "; 
	cin >>  response; 
	while ( response == 1 ) 
	{ 
		current = current ->  next = new Elephant; 
		cout  << "\nNAME: "; 
		cin >>  current ->  name; 
		cout  << "\nAdd another? (1 == yes, 0 == no): "; 
		cin >>  response; 
	} 
	current -> next = 0; 

	return first; 
} 


void print_elephants( const Elephant* ptr )//打印 
{ 
	int count = 1; 
	cout  << "\n\n\n"; 
	while ( ptr !=  0 ) { 
		cout  << "Elephant number "  << count++ 
			<< " is "  << ptr ->  name  << '\n'; 
		ptr = ptr ->  next; 
	} 
} 

void free_list( const Elephant* ptr )//释放 
{ 
	const Elephant* temp_ptr; 
	while ( ptr !=  0 )  
	{ 
		cout <<"1111111111111111" <<endl; 
		temp_ptr = ptr ->  next; 
		delete ptr; 
		ptr = temp_ptr; 
	} 
} 

[baihacker]

别人是问成功的原因,你自己看他的注释

[夜雨_倚琴]

print_elephants( start );
start是指针类型没错, 但是 传递到 void print_elephants( const Elephant* ptr ) 里时候 ptr = start.
之后在print_elephants调用的时候 ptr的值 会改变, 显然 start值 不会变.

如果你想让start变化的话,可以将打印函数声明为:
void print_elephants( const Elephant& *ptr );

44看吧!

[夜雨_倚琴]

不好意思!
修改start的值,应该将声明改为:
void print_elephants( const Elephant *&ptr );

[tianma2005123]

看看高质量一文.

[IT_lau]

传的是指针的一个引用,所以不回改变start的指向

[zcl198715]

非常谢谢!

[HelloDan]

搞笑，上面的两位

[chowming]

传递的是值吧