How do I print boolean values with boost::format as symbolic values?
Can this be done without boost::io::group? It seems that flags sent to the stream beforehand get retested:
#include <iomanip>
#include <iostream>
#include <boost/format.hpp>
int main()
{
std::cout
<< std::boolalpha
<< true << " "
<< boost::format("%1% %2%\n")
% true
% boost::io::group(std::boolalpha, true)
;
}
Output
true 1 true
You can archive that like this:
#include <iomanip>
#include <iostream>
#include <boost/format.hpp>
int main()
{
std::cout
<< std::boolalpha
<< true << " "
<< boost::format("%1$b %2%\n")
% true
% boost::io::group(std::boolalpha, true)
;
}
It doesn't appear to me that you can.
I looked at the Boost.Format documentation and the code, and didn't see anything.
On the other hand, the sample code shows how to write a formatter for a user-defined type. You could write one for "bool"
Related
I print a bool to an output stream like this:
#include <iostream>
int main()
{
std::cout << false << std::endl;
}
Does the standard require a specific result on the stream (e.g. 0 for false)?
The standard streams have a boolalpha flag that determines what gets displayed -- when it's false, they'll display as 0 and 1. When it's true, they'll display as false and true.
There's also an std::boolalpha manipulator to set the flag, so this:
#include <iostream>
#include <iomanip>
int main() {
std::cout<<false<<"\n";
std::cout << std::boolalpha;
std::cout<<false<<"\n";
return 0;
}
...produces output like:
0
false
For what it's worth, the actual word produced when boolalpha is set to true is localized--that is, <locale> has a num_put category that handles numeric conversions, so if you imbue a stream with the right locale, it can/will print out true and false as they're represented in that locale. For example,
#include <iostream>
#include <iomanip>
#include <locale>
int main() {
std::cout.imbue(std::locale("fr"));
std::cout << false << "\n";
std::cout << std::boolalpha;
std::cout << false << "\n";
return 0;
}
...and at least in theory (assuming your compiler/standard library accept "fr" as an identifier for "French") it might print out faux instead of false. I should add, however, that real support for this is uneven at best--even the Dinkumware/Microsoft library (usually quite good in this respect) prints false for every language I've checked.
The names that get used are defined in a numpunct facet though, so if you really want them to print out correctly for particular language, you can create a numpunct facet to do that. For example, one that (I believe) is at least reasonably accurate for French would look like this:
#include <array>
#include <string>
#include <locale>
#include <ios>
#include <iostream>
class my_fr : public std::numpunct< char > {
protected:
char do_decimal_point() const { return ','; }
char do_thousands_sep() const { return '.'; }
std::string do_grouping() const { return "\3"; }
std::string do_truename() const { return "vrai"; }
std::string do_falsename() const { return "faux"; }
};
int main() {
std::cout.imbue(std::locale(std::locale(), new my_fr));
std::cout << false << "\n";
std::cout << std::boolalpha;
std::cout << false << "\n";
return 0;
}
And the result is (as you'd probably expect):
0
faux
0 will get printed.
As in C++ true refers to 1 and false refers to 0.
In case, you want to print false instead of 0,then you have to sets the boolalpha format flag for the str stream.
When the boolalpha format flag is set, bool values are inserted/extracted by their textual representation: either true or false, instead of integral values.
#include <iostream>
int main()
{
std::cout << std::boolalpha << false << std::endl;
}
output:
false
IDEONE
my code:
#include <iostream>
#include <iomanip>
using namespace std;
int main() {
double A = 100.35;
cout.precision(0);
cout << std::hexfloat << std::fixed << std::left << A << endl;
return 0;
}
Current output:
100
my expected output:
x64
Explanation:
I want to print the hex value of decimal part of double. But I have been unsuccessful in getting this. need help. Any help in this direction will be appreciated.
What you're asking for is simply not possible. std::hex (the output you're looking for) only works for integral arguments, and std::hexfloat uses an undesirable format. You need to cast or round.
#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main() {
double A = 100.35;
cout.precision(0);
cout << std::hex << std::showbase << std::lround(A) << endl;
return 0;
}
I have a problem using atof,
here is the code:
#include <stdio.h>
#include <cstdlib>
#include <iostream>
#include <string>
using namespace std;
int main(){
std::string num ("1.0");
//std::string num ("1.1");
cout<< atof(num.c_str());
return 0;
}
If the num string is "1.1" , it can correctly cout 1.1. But if I want to keep the zero when the num string is "1.0" (want it to be 1.0 but not 1), what should I do?
You need to use std::fixed and std::setprecision, like so:
std::cout<< std::fixed << std::setprecision(1) << atof(num.c_str());
This will require that you include the iomanip header.
A possible solution is
#include <cstdio>
#include <iostream>
#include <string>
#include <iomanip>
int main() {
std::cout.precision(3);
std::cout.setf(std::ios::fixed);
std::string s("1.0");
float f = 0.0f;
sscanf(s.c_str(), "%f", &f);
// alternative way of setting this flags
// std::cout << std::fixed << std::setprecision(3) << f << "\n";
std::cout << f << "\n";
return (0);
}
notice that there are at least 2 ways of accomplishing the same format for the output, I left one of them commented out .
I print a bool to an output stream like this:
#include <iostream>
int main()
{
std::cout << false << std::endl;
}
Does the standard require a specific result on the stream (e.g. 0 for false)?
The standard streams have a boolalpha flag that determines what gets displayed -- when it's false, they'll display as 0 and 1. When it's true, they'll display as false and true.
There's also an std::boolalpha manipulator to set the flag, so this:
#include <iostream>
#include <iomanip>
int main() {
std::cout<<false<<"\n";
std::cout << std::boolalpha;
std::cout<<false<<"\n";
return 0;
}
...produces output like:
0
false
For what it's worth, the actual word produced when boolalpha is set to true is localized--that is, <locale> has a num_put category that handles numeric conversions, so if you imbue a stream with the right locale, it can/will print out true and false as they're represented in that locale. For example,
#include <iostream>
#include <iomanip>
#include <locale>
int main() {
std::cout.imbue(std::locale("fr"));
std::cout << false << "\n";
std::cout << std::boolalpha;
std::cout << false << "\n";
return 0;
}
...and at least in theory (assuming your compiler/standard library accept "fr" as an identifier for "French") it might print out faux instead of false. I should add, however, that real support for this is uneven at best--even the Dinkumware/Microsoft library (usually quite good in this respect) prints false for every language I've checked.
The names that get used are defined in a numpunct facet though, so if you really want them to print out correctly for particular language, you can create a numpunct facet to do that. For example, one that (I believe) is at least reasonably accurate for French would look like this:
#include <array>
#include <string>
#include <locale>
#include <ios>
#include <iostream>
class my_fr : public std::numpunct< char > {
protected:
char do_decimal_point() const { return ','; }
char do_thousands_sep() const { return '.'; }
std::string do_grouping() const { return "\3"; }
std::string do_truename() const { return "vrai"; }
std::string do_falsename() const { return "faux"; }
};
int main() {
std::cout.imbue(std::locale(std::locale(), new my_fr));
std::cout << false << "\n";
std::cout << std::boolalpha;
std::cout << false << "\n";
return 0;
}
And the result is (as you'd probably expect):
0
faux
0 will get printed.
As in C++ true refers to 1 and false refers to 0.
In case, you want to print false instead of 0,then you have to sets the boolalpha format flag for the str stream.
When the boolalpha format flag is set, bool values are inserted/extracted by their textual representation: either true or false, instead of integral values.
#include <iostream>
int main()
{
std::cout << std::boolalpha << false << std::endl;
}
output:
false
IDEONE
I want to know how can I make the string I converted from DWORD to onstringstream and then to AnsiString.
But that doesn't really matter, the conversion could be from int to string, I just want to know how I can make every string converted to ALWAYS show 6 digits, like if my number is 57, in the string it will be 000057.
Thanks!
Use io manipulators setfill and setw:
#include <iostream>
#include <string>
#include <sstream>
#include <iomanip>
int main()
{
std::ostringstream s;
s << std::setfill('0') << std::setw(6) << 154;
std::cout << s.str() << "\n";
return 0;
}
So, the question about formatted output?
you can use iostream::width and `iostream::fill':
// field width
#include <iostream>
using namespace std;
int main () {
cout << 100 << endl;
cout.width(6);
cout.fill('0');
cout << 100 << endl;
return 0;
}