Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help 
std::ios_base::width(3)	      C++ Standard Libary      std::ios_base::width(3)

NAME
       std::ios_base::width - std::ios_base::width

Synopsis
	  streamsize width() const;		    (1)
	  streamsize width( streamsize new_width ); (2)

	  Manages the minimum number of	characters to generate on certain out-
       put operations
	  and  the  maximum  number of characters to generate on certain input
       operations.

	  1) Returns the current field width.
	  2) Sets the field width to the given one. Returns the	previous field
       width.

Parameters
	  new_width - new field	width setting

Return value
	  The field width before the call to the function

Notes
	  Some I/O functions call width(0)  before  returning,	see  std::setw
       (this results in
	  this	field  having effect on	the next I/O function only, and	not on
       any subsequent
	  I/O)

	  The exact effects this modifier has on the input and output vary be-
       tween the
	  individual I/O functions and are described at	 each  operator<<  and
       operator>>
	  overload page	individually.

Example
       // Run this code

	#include <array>
	#include <tuple>
	#include <ctime>
	#include <string>
	#include <iostream>
	#include <sstream>
	#include <iomanip>

	int main()
	{
	    auto str_time = [](int year, int mon, int day)
	    {
		constexpr std::array<const char*, 7> week_day{ {
		    "Sunday",  "Monday",  "Tuesday",  "Wednesday", "Thursday",
       "Friday", "Saturday"
		} };

		std::tm	tm{};
		tm.tm_year = year - 1900;
		tm.tm_mon  = mon - 1;
		tm.tm_mday = day;

		day += mon < 3 ? year--	: year - 2;
		tm.tm_wday = (23 * mon / 9 + day + 4 + year / 4	- year / 100 +
       year / 400) % 7;

		std::ostringstream out;
		out << week_day[tm.tm_wday] << ", " << std::put_time(&tm,  "%B
       %d, %Y");
		return out.str();
	    };

	    constexpr int column_size =	4;
	    using table_t = std::array<std::string, column_size>;

	    table_t  headers{  {  "Name", "Birthdate", "Death date", "Language
       Created"	} };

	    std::array<table_t,	5> data{ {
		{ { "Dennis Ritchie", str_time(1941, 9,	9), str_time(2011, 10,
       12), "C"	} },
		{ { "Bjarne Stroustrup", str_time(1950,	12, 30), "",  "C++"  }
       },
		{ { "Anders Hejlsberg",	str_time(1960, 12, 2), "", "C#"	} },
		{  { "Guido van	Rossum", str_time(1956,	1, 31),	"", "Python" }
       },
		{ { "Brendan Eich", str_time(1961, 7, 4), "", "Javascript" } }
	    } };

	    constexpr int name_wid  = 20;
	    constexpr int birth_wid = 30;
	    constexpr int death_wid = 30;
	    constexpr int lang_wid  = 18;

	    auto print_line = [](table_t const &tbl)
	    {

		auto const &[Name, Birthdate,  DeathDate,  LanguageCreated]  =
       tbl;

		std::cout.width(name_wid);
		std::cout << ("| " + Name) << '|';

		std::cout.width(birth_wid);
		std::cout << ('	' + Birthdate) << '|';

		std::cout.width(death_wid);
		std::cout << ('	' + DeathDate) << '|';

		std::cout.width(lang_wid);
		std::cout << ('	' + LanguageCreated) <<	'|';

		std::cout << '\n';
	    };

	    constexpr  int  total_wid  =  name_wid  +  birth_wid + death_wid +
       lang_wid	+ column_size;

	    auto print_break = []
	    {
		std::cout.width(total_wid);
		std::cout.fill('-');
		std::cout << '-' << '\n';
		std::cout.fill(' ');
	    };

	    std::cout.setf(std::ios::left, std::ios::adjustfield);
	    print_break();
	    print_line(headers);
	    print_break();
	    for	(auto const &entry : data)
		print_line(entry);
	    print_break();
	}

Output:
	------------------------------------------------------------------------------------------------------
	|  Name		      |	 Birthdate		       |  Death	  date
       | Language Created |
	------------------------------------------------------------------------------------------------------
	|  Dennis Ritchie    | Tuesday,	September 09, 1941  | Wednesday, Octo-
       ber 12, 2011  | C		|
	|   Bjarne   Stroustrup	  |   Saturday,	  December   30,    1950     |
       | C++		  |
	|    Anders    Hejlsberg    |	Friday,	  December   02,   1960	     |
       | C#		  |
	|   Guido   van	  Rossum    |	Tuesday,   January   31,   1956	     |
       | Python		  |
	|    Brendan	Eich	    |	Tuesday,   July	  04,	1961	     |
       | Javascript	  |
	------------------------------------------------------------------------------------------------------

See also
	  precision manages decimal precision of floating point	operations
		    (public member function)

http://cppreference.com		  2022.07.31	       std::ios_base::width(3)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=std::ios_base::width&sektion=3&manpath=FreeBSD+Ports+15.0>

home | help