modify the value in pair<>

[timothyguo]

vector< pair<string, double> > var_map;

...here pushes pairs into var_map...

var_map.back().second = 4.3;

why can the last line not modify the value stored in the last element of var_map?
What is the right way to do that?

[kbw]

why can the last line not modify the value stored in the last element of var_map?

It ought to.

What is the right way to do that?

Looks ok to me, as long as the vector isn't empty.

[jsmith]

This works for me:

#include <string>
#include <utility>
#include <vector>
#include <iostream>

int main() {
    std::vector< std::pair< std::string, double > > var_map;
    var_map.push_back( std::make_pair( std::string( "Hello" ), 3.14 ) );
    var_map.back().second = 1.414;
    std::cout << var_map.back().first << " -> " << var_map.back().second << std::endl;
}

[timothyguo]

Oh! I made a mistake somewhere else. :-(