Couple Questions!

[Anmol444]

Does ios stand for Input/Output Supervisor?

Also in this code

cout << std::setiosflags(std::ios::left);

Does that mean that ios is a namespace inside of std?

And a flag is just a Boolean that can be set off or on, in this case it modifies the output stream if it is on or off?

In this link: http://msdn.microsoft.com/en-us/library/943z481t(v=vs.110).aspx

I dont understand the return type, can anyone please explain!

[Cubbi]

It stands for input/output stream.

std::ios is a typedef for std::basic_ios<char> which is a class that is publicly derived from std::ios_base, which is a class that has a public static member constant called "left"

You could have written std::cout << std::setiosflags(std::ios_base::left); for the same effect, or just std::cout << std::left; (there is a slight difference in that setiosflags resets all flags, while std::left only affects the adjustment flags)

As for the return type, it's just low-level machinery behind the I/O manipulators: those manipulators that take arguments (like setw or this setiosflags) are functions that return objects of unspecified type that have operator<< or operator>> overloads to apply the changes to the stream.

[Anmol444]

Setiosflags resets all the flags?

Also if it is a class why do you use :: to access it and not .?


Oh ok thanks for the return type thing.

[Cubbi]

You use :: to access static member of a class:

#include <iostream>
struct A { 
    static const int example = 1;
};
int main()
{
    std::cout << A::example << '\n';
}

[Anmol444]

You cant use .?

Or do you use :: so that it doesnt create a new class?

[Cubbi]

Yes, you can use the dot if you have an object of that class. For your case, std::cout works:

#include <iostream>
#include <iomanip>
int main()
{
    std::cout << std::setiosflags(std::cout.left);
}

it's more common to use :: to indicate that what you're accessing is a static

[Anmol444]

Oh I got it so you use :: to indicate you are accessing a static, and it can be used without creating a new member of the class.

Also what do you mean it resets all flags, and I am still a bit confused with the return type, what is str?

[Cubbi]

Setiosflags resets all the flags?

I didn't phrase that right, std::setiosflags() can set all formatting flags, e.g. hex, uppercase, and left at once. std::left/std::right/std::internal only affect adjustments.

[Cubbi]

am still a bit confused with the return type, what is str?

str is just the name given by MSDN documentation to the stream (std::cout in your case).

returns an object that, when extracted from or inserted into the stream str, calls str.setf(_Mask), and then returns str.

This says that, given

auto object = std::setprecision(std::ios::left);
std::ostream& str = std::cout;

the following two lines do the same thing

str << object;
str.setf(std::ios::left)

[Anmol444]

What do you mean only affects adjustments? Also std::left, what is left a function or what is it?

Also do I have flags right, a Boolean value?

[Cubbi]

std::left is an I/O manipulator that you can use instead of the much longer (and potentially ambiguous) std::setiosflags(std::ios::left). Like all I/O manipulators, it's a template function.

do I have flags right, a Boolean value

They are bits in a bitmask. E.g, in LLVM libc++
http://llvm.org/svn/llvm-project/libcxx/trunk/include/ios

class ios_base
{
public:
    typedef unsigned int fmtflags;
    static const fmtflags left        = 0x0020;
    static const fmtflags right       = 0x0080;
...

[Anmol444]

One more question, the setw manipulator only acts on the next object to be outputted right?

[Cubbi]

Simply put, yes. To be precise, it changes the field with value in the stream object, and most I/O operators change it back to zero. The full list of width-resetting operations is here: http://en.cppreference.com/w/cpp/io/manip/setw

[Anmol444]

What do you mean bitmask?

[cire]

Hello google.

[Anmol444]

I tried google, I found a link to wikipedia: http://en.wikipedia.org/wiki/Mask_(computing)

So basically a bitmask is any data the bitwise operators can operate on?

And the Flag is a bool type (1 byte) so it can only be set to true or false.

[Anmol444]

Im still confused on the return type but i'll just ignore it for now.

[Anmol444]

Also by adjustments you mean it only affects what its meant to do?

[Anmol444]

Can you please help cire or anyone, is a bitmask any data the bitwise operators can operate on?

And a Flag is a bool type (1 byte) so it can only be set to true or false?

[cire]

A bitmask is a pattern of bits. A bitmask can be used to set, check or clear a bit pattern depending on which bitwise manipulation is used. The smallest representation we can manipulate that can be used to indicate true or false (1 or 0) is a bit, so a bit may be referred to as a flag.

The following program checks to see which bits are set in an unsigned int. It's pretty basic and I would encourage you to check out the bitwise operators and play around with this before you ask further questions.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

#include <limits> #include <iostream> class Binary { public: Binary(unsigned value) : _value(value) {} operator unsigned() { return _value ; } private: unsigned _value ; }; std::ostream& operator<<(std::ostream& os, Binary b) { unsigned bitmask = 1u << (std::numeric_limits<unsigned>::digits-1u) ; while ( bitmask ) { os << ((b & bitmask) != 0) ; bitmask >>= 1 ; } return os ; } int main() { unsigned n ; while ( (std::cout << "Enter a number: ") && (std::cin >> n) ) std::cout << Binary(n) << '\n' ; }

Enter a number: 2 00000000000000000000000000000010 Enter a number: 4 00000000000000000000000000000100 Enter a number: 8 00000000000000000000000000001000 Enter a number: 6 00000000000000000000000000000110 Enter a number: 12 00000000000000000000000000001100 Enter a number: 14 00000000000000000000000000001110 Enter a number: 15 00000000000000000000000000001111 Enter a number: 16 00000000000000000000000000010000 Enter a number: