String to double problem

it may be the display of the value, not the actual value itself that's the problem. Try adjusting the display with ostream modifiers like setprecision, setwidth, etc.

Thanks, now it displays correctly!
But, i save this values in a file:

double sec;
               double secundo;

                seconds = str.substr(19,10);
		istringstream(seconds) >> sec;
		cout.precision(10);
		cout.setf(ios::fixed, ios::floatfield);
		cout << "sec: " << sec << endl;
		
		secundo = ((min*60)+sec);
		cout << secundo<< endl;
		frames[i].timesec = secundo;
}

myfile.open ("Exemplo.csv", ios::out | ios::app);
	myfile << "Frame.time_delta" << ";" << "Frame.timesec" << ";" << "Frame.lenght" << ";" << endl;
	
	for(i=1; i<= k ; i++)
	{ 
		myfile << frames[i].time_delta << ";" << frames[i].timesec << ";" << frames[i].lenght << endl;
	}

Secundo is also displaying right, but when i save into a file the value is displayed without the .precision(10), how do i instruct to save with the same precision?

myfile.precision(10); should do the trick I think, filestreams are very similar to cout and cin.

Thanks, it works!!!