I am new to C++ and I was wondering how I can understand what functions and classes do. For example I was told to use "istringstream" for a homework assignment. I have looked online and found the site cplusplus.com with a lot of references. The problem I have is understanding the reference page.
On the "istringstream" reference page I am given the following code:
// istringstream constructors.
#include <iostream> // std::cout
#include <sstream> // std::istringstream
#include <string> // std::string
int main () {
std::string stringvalues = "125 320 512 750 333";
std::istringstream iss (stringvalues);
for (int n=0; n<5; n++)
{
int val;
iss >> val;
std::cout << val*2 << '\n';
}
return 0;
}
In the code above, it does exactly what I need it to do for my assignment but I do not understand WHY it works. So they created a istringstream object called iss, then later used "iss >> val". That is the part I am confused with. What exactly does it do?
I have tried reading the text above where it explains what each function in the class does but I did not understand any of it. For example, one of the first lines on the reference page says
default (1) explicit istringstream (ios_base::openmode which = ios_base::in);
How do I interpret this line? From what I can see it is a function that takes one argument but what is "ios_base::openmode which = ios_base::in".
I believe this is the page you're looking for. This defines that mysterious >> operator. It is overloaded several different ways, which means it's working like a scanf function for several different data types.
Your compiler looks at iss >> val and says "Hmm...iss is an istringstream and val is an int. Aha! Looks like istringstream has an operator>> that takes an int&, I'll use that!"
Edit: istream has an operator>> for int&. istringstream inherits those.