limits for reading inputlines

hello

I am having problems with reading input lines.
i wanna tell my progrem that whan i input a line it have to read diferent strings.

if i input a line:
n10000 x-123 465 y

i have to get this
string strn ( line , 'n' , 'x');
string strx (line , 'x' , 'y');
cout << " n = " << strn <<endl;
cout << " x = " << strx << endl;

so when i run a program i shuld get this output:
n = 10000
x = -123465
it wont work couse the start of astring is wrong why
here is my

Code:

#include <iostream>
#include <string>
#include <sstream>

using namespace std;


int main()
{
    string str;
    cout << "Enter a number: ";
    getline(cin, str);

    stringstream ss;
    string s4 ( str , 'n' , 'x'); //if i write a number instead of 'n' it will work and start reading
    string s5 (str , 'x' , 'y');
    ss << s4 ;
cout << " s4 = " << s4 << endl;
cout << " s5  =  " << s5 <<endl ;
//int i;
//ss >> i;
    //int i;
   // if ( ss >> i )
   //     cout << "Valid conversion to int:\n " << i <<"\n";
   //    cout << " i + 100 =  " << ( i + 100)<<endl;
/*else
        cout << "Invalid input";
}
*/
}

The entire line is read in to str. You are trying to separate it by the characters 'n', 'x', and 'y'. However, I don't think the string constructor works like that. I think you have to call find to find the location of those characters and then substr to get a substring between them.