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 output 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 between 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, October 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)