string长度计算问题

[小利]

如题，下面是代码，为什么打印出来tmp.length()不是我想要的长度？

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int
main()
{
	string str = "";
	string tmp = "";

	ifstream in("test.txt");

	while(getline(in, str))
	{
		cout<<str.length()<<" "<<str<<endl;
		
		for(int i = 0; i < str.length(); i++)
		{
			cout<<std::hex<<(int)str[i]<<" ";
			tmp.append(&str[i]);
		}
		cout<<endl<<tmp.length()<<"----"<<tmp<<"----"<<endl;
		tmp = "";
	}
	
	in.close();
	
	return 0;
}

[Jim_King_2000]

1. 是不是应该去掉取地址符？ tmp.append(str[i]);
2. in.close()不需要显示调用，析够会关闭文件。

[ppsharp]

不是str.size()吗？

[Eleven]

你的tmp.append(&str[i]);这里不对

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int
main()
{
    string str = "";
    string tmp = "";
	
    ifstream in("F:\\11.txt");
	char buf[2] = {0};
	
    while(getline(in, str))
    {
        cout<<str.length()<<" "<<str<<endl;
        
        for(int i = 0; i < str.length(); i++)
        {
            cout<<std::hex<<(int)str[i]<<" ";
			buf[0] = str[i];
            tmp.append(buf);
        }
        cout<<endl<<tmp.length()<<"----"<<tmp<<"----"<<endl;
        tmp = "";
    }
    
    in.close();
    
    return 0;
}

[Qyee16]

tmp.append(&str[i]); 你传递的是地址哦。亲

[xs574924427]

你append的是地址

[小利]

为什么要用buf？
不用不行么？
直接tmp.append(str[i])？？？

[Quote=引用 3 楼 visualeleven 的回复:]

你的tmp.append(&str[i]);这里不对
C/C++ code

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int
main()
{
string str = "";
……
[/Quote]

[JoeBlackzqq]

#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main()
{
    string str = "";
    string tmp = "";
	
    ifstream in("test.txt");
	
    while(getline(in, str))
    {
        cout<<str.length()<<" "<<str<<endl;
        
        for(int i = 0; i < str.length(); i++)
        {
            cout<<std::hex<<(int)str[i]<<" ";
            tmp.append(&str[i], 1);	// 添加一个字符(默认是添加字符串的)
        }
		cout<<std::dec;			// 返回到十进制输出
		//cout<<endl<<endl;
        cout<<endl<<tmp.length()<<"----"<<tmp<<"----"<<endl<<endl;
        tmp = "";
    }
    
    in.close();
    
    return 0;
}

[JoeBlackzqq]

basic_string::append
basic_string& append(const E *s);
basic_string& append(const E *s, size_type n);
basic_string& append(const basic_string& str,
size_type pos, size_type n);
basic_string& append(const basic_string& str);
basic_string& append(size_type n, E c);
basic_string& append(const_iterator first, const_iterator last);
The member template function appends the operand sequence to the end of the sequence controlled by *this, then returns *this.

In this implementation, if a translator does not support member template functions, the template:

template<class InIt>
basic_string& append(InIt first, InIt last);
is replaced by:

basic_string& append(const_iterator first, const_iterator last);
See the related sample program.