Width and setfill('-') in cpp-CodePudding

I am new to C and am wondering if there is a more elegant way to print out the following:

Celsius  Kelvin  Fahrenheit  Reaumur
-------------------------------------

I guess you could just do

cout << "Celsius  Kelvin  Fahrenheit  Reaumur" << endl << "-------------------------------------";

But it doesn't look good. In Ada you could do "Width". Is there a similiar operator in cpp? And can you not just do setfill('-') and the amount of '-' you want to print out?

Any help is greatly appreciated

CodePudding user response：

Here are two other ways to produce this line:

    std::cout << "-------------------------------------\n";

std::setfill std::setw:

#include <iomanip>

    std::cout << std::setfill('-') << std::setw(38) << '\n';

Using a std::string:

#include <string>

    std::cout << std::string(37, '-') << '\n';

Demo

CodePudding user response：

You could (and probably should) use std::format. Also see the fmtlib/fmt library:

Both format and fmtlib use the format spec':

https://en.cppreference.com/w/cpp/utility/format/format

Also see this question which features several related answers:

std::string formatting like sprintf

You can tweak this very easily to make this fit your needs (I made some deliberate imperfections for the sake of clarity):

#include <fmt/core.h>

int main() {
    int const width = 12;

    // See https://en.cppreference.com/w/cpp/utility/format/format
    // ^ centres the field (with default space fill)
    // -^ centres the field with "-" fill
    // 12 and 52 are specific field widths.
    // inner {} means the field width is provided by the next parameter

    fmt::print("_{:^{}} {:^{}} {:^{}} {:^12}_\n-{:-^52}\n", 
            "Celsius", width,
            "Kelvin", width,
            "Farenheit", width,
            "Reaumur",
            "=");
}

Output:

_  Celsius       Kelvin     Farenheit     Reaumur   _
--------------------------=--------------------------

FmtLib Demo: https://godbolt.org/z/463xWvx5P

Format Demo: https://godbolt.org/z/MP9sac7ba (thanks Ted)

CodePudding user response：

Big fan of separating this out for re-use and easier reading. Example:

std::ostream & draw_heading(std::ostream & out,
                            const std::string & heading)
{
    char old_fill = out.fill('-');
    std::streamsize old_width = out.width();
    out << h.mHeading << '\n'
        << std::setw(h.mHeading.size()   1) << '\n';
    out.width(old_width);
    out.fill(old_fill);
    return out;
}

Only does the writing and will write to any output stream. It returns a reference to the stream so it can be easily tested for success or chained.

Basic Usage:

draw_heading(std::cout, "Celsius  Kelvin  Fahrenheit  Reaumur");

The ugly stuff is now buried away from the main logic, which can get on with whatever the heck its job is.

CodePudding user response：

You can use the literal string feature:

#include <string>
#include <iostream>

int main()
{
    std::cout << R"(
This is a line of text with an underline
----------------------------------------
)";

}

This allows you to add all the explicit characters you want (including newline) which makes the layout of large chunks of text nicer (relatively) to do in code.

I just wish that the R"( ignored the first newline if it is the only character on that line. But it still looks better than:

cout << "Celsius  Kelvin  Fahrenheit  Reaumur\n"
     << "------------------------------------\n";

cout << "Celsius  Kelvin  Fahrenheit  Reaumur\n"
     << std::string(38, '-') << "\n";