C++ Iomanip lib setfill and setw issues - c++

Question

My Code:
#include <iostream>
#include <iomanip>
using namespace std;
int main () {
int time;
int honolulu, seattle, london, moscow, hongkong, auckland;
cout << "What is the current time in Philadelphia? ";
cin >> time;
honolulu = (time+2400-600)%2400;
seattle = (time+2400-300)%2400;
london = (time+2400+500)%2400;
moscow = (time+2400+800)%2400;
hongkong = (time+2400+1200)%2400;
auckland = (time+2400+1700)%2400;
cout << endl << "Current times in other cities: " << endl;
cout << setw (12) << left << "Honolulu:";
cout << setw (4) << setfill('0') << honolulu << endl;
cout << setw (12) << left << "Seattle:";
cout << setw (4) << setfill('0') << seattle << endl;
cout << setw (12) << left << "London:";
cout << setw (4) << setfill('0') << london << endl;
cout << setw (12) << left << "Moscow:";
cout << setw (4) << setfill('0') << moscow << endl;
cout << setw (12) << left << "Hong Kong:";
cout << setw (4) << setfill('0') << hongkong << endl;
cout << setw (12) << left << "Auckland:";
cout << setw (4) << setfill('0') << auckland << endl;
return 0;
}
Required Output :
What is the current time in Philadelphia? 0415
Current times in other cities:
Honolulu: 2215
Seattle: 1150
London: 9150
Moscow: 1215
Hong Kong: 1615
Auckland: 2115
My output :
What is the current time in Philadelphia? 0415
Current times in other cities:
Honolulu: 2215
Seattle:00001150
London:000009150
Moscow:000001215
Hong Kong:001615
Auckland:0002115
What am I doing wrong? The first line of output, Honolulu: 2215, is correct. But the next lines have leading zeroes. I do not understand why this is happening? Is there a problem with my code or am I misunderstanding how the functions setfill and setw work?

Answer 1

The fill character is "sticky", so it remains in effect until you change it.
In your case, you want 0 as the fill for the numeric fields, but space as the fill for the character fields, so you'll have to set that explicitly, something like this:
cout << setfill(' ') << setw (12) << left << "Seattle:";

Answer 2

Many of the iomanip objects are "sticky", that is, they stick to the stream and affect subsequent lines.
When you have this:
cout << setw (12) << left << "Seattle:";
cout << setw (4) << setfill('0') << seattle << endl;
that is going to leave the setfill active for the next line. So you might instead prefer
cout << setw (12) << setfill(' ') << left << "Seattle:";
cout << setw (4) << setfill('0') << seattle << endl;

Answer 3

As mentioned in other comments many of I/O manipulators are "sticky".
I personally prefer to solve this kind of problem using RAII:
class stream_format_raii {
public:
stream_format_raii(std::ostream &stream)
: stream_(stream)
, state_(NULL) {
state_.copyfmt(stream_);
}
~stream_format_raii() {
stream_.copyfmt(state_);
}
public:
std::ostream &stream_;
std::ios state_;
};
That this class does is backing up your current stream's format upon constructing and setting it back upon destructing.
You can use it this way:
void printCity(std::ostream &os, const std::string name, int time) {
stream_format_raii back(os);
os << std::setw(12) << std::left << (name + ":");
os << std::setw(4) << std::setfill('0') << time;
}
int main() {
// Same as before
printCity(std::cout, "Honolulu", honolulu);
// Same as before
}