std::ios_base::width(3)

hey bestie!! welcome to std::ios_base::width from the C++ Standard Libary manual 💖✨ (yes, the manual name is literally C++ Standard Libary, typo and all — iykyk 😭💅). okay so this page is all about controlling field width, and it's lowkey iconic.

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🌸 NAME 🌸

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

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✨ Synopsis ✨

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

This little icon manages the minimum number of characters to generate on certain output operations and the maximum number of characters to generate on certain input operations. It's giving field-width control, no cap 💅.

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

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🎀 Parameters 🎀

• new_width — new field width setting

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🌈 Return value 🌈

The field width before the call to the function. That's the vibe 🫶.

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🦋 Notes 🦋

Heads up, bestie: 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). So don't expect it to stick around like a main character, okay? 😭

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. Periodt.

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💻 Example 💻

// Run this code

#include <algorithm>
#include <array>
#include <iomanip>
#include <iostream>
#include <span>
#include <string_view>
using namespace std::string_view_literals;

constexpr std::array table_header =
{
    "Language"sv, "Author"sv, "Birthdate"sv, "RIP date"sv
};

using row_t = std::array<std::string_view, table_header.size()>;
using widths_t = std::array<std::size_t, table_header.size()>;

constexpr std::array table_body = std::to_array<row_t>
({
    {"C", "Dennis Ritchie", "1941-09-09", "2011-10-12"},
    {"C++", "Bjarne Stroustrup", "1950-12-30"},
    {"C#", "Anders Hejlsberg", "1960-12-02"},
    {"Python", "Guido van Rossum", "1956-01-31"},
    {"Javascript", "Brendan Eich", "1961-07-04"}
});

constexpr widths_t calculate_column_widths(std::span<const row_t>
       table)
{
    widths_t widths{};
    for (const row_t& row : table)
        for (size_t i = 0; i != row.size(); ++i)
            widths[i] = std::max(widths[i], row[i].size());
    return widths;
}

void print_row(const row_t& row, const widths_t& widths)
{
    std::cout << '|';
    for (size_t i = 0; i != row.size(); ++i)
    {
        std::cout << ' ';
        std::cout.width(widths[i]);
        std::cout << row[i] << " |";
    }
    std::cout << '\n';
};

void print_break(const widths_t& widths)
{
    const std::size_t margin = 1;
    std::cout.put('+').fill('-');
    for (std::size_t w : widths)
    {
        std::cout.width(w + margin * 2);
        std::cout << '-' << '+';
    }
    std::cout.put('\n').fill(' ');
};

int main()
{
    constexpr widths_t widths = calculate_column_widths(table_body);

    std::cout.setf(std::ios::left, std::ios::adjustfield);
    print_break(widths);
    print_row(table_header, widths);
    print_break(widths);
    for (const row_t& row : table_body)
        print_row(row, widths);
    print_break(widths);
}

✨ Output: ✨

+------------+-------------------+------------+------------+
| Language   | Author            | Birthdate  | RIP date   |
+------------+-------------------+------------+------------+
| C          | Dennis Ritchie    | 1941-09-09 | 2011-10-12 |
| C++        | Bjarne Stroustrup | 1950-12-30 |            |
| C#         | Anders Hejlsberg  | 1960-12-02 |            |
| Python     | Guido van Rossum  | 1956-01-31 |            |
| Javascript | Brendan Eich      | 1961-07-04 |            |
+------------+-------------------+------------+------------+

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👀 See also 👀

• precision — manages decimal precision of floating point operations (public member function)
• setw — changes the width of the next input/output field (function)

okay bestie, that's the whole page! big slay energy, no cap 💅✨ — source/version/date: http://cppreference.com · 2024.06.10 · std::ios_base::width(3) 🫶🎀