Question

Hi I have vector of strings,that is the structure of vector : The name of vector is vector

"key:  abc 165.123.34.12", 
"key:  bca 1.1.1.1", 
"key1: bac 3.3.3.3"

I want to sort the vector according to the second field(abc,bac,bac)

My code is;

 bool sort_function(string& str1,string& str2) {

     string nick1,nick2,nick1_ignore,nick2_ignore;

     stringstream ss1(str1) 

     ss1>> nick1_ignore >> nick1;

     stringstream ss2(str2) 

     ss2>> nick2_ignore >> nick2;

     return (nick1<nick2);

 }


     sort(vector.begin(), vector.end(),sort_function);

But it gives a long error starting with error,

  error: no match for ‘operator>>’ in ‘std::basic_stringstream<char>

UPDATE:Error is tl_algo.h: In function ‘_RandomAccessIterator std:..

UPDATE:It is fixed. the error is in function declaration I have to use const string

Answer 1

The function template overload operator>>(std::basic_istream &, std::string &) is non-const on its istream parameter, so you can’t call it on a temporary.

This is confusing, because you can call the member operator>> when reading a primitive e.g. int.

Instead, you’ll have to write

stringstream ss1(str1); ss1 >> nick1_ignore >> nick1;

You could also work around this by first reading a no-op manipulator or calling a no-op method to get an lvalue reference:

stringstream(str1).ignore(0) >> nick1_ignore >> nick1;

C++11 fixes this by providing overloads of the free operator>> with the istream parameter an rvalue reference.