Setting text color of the Windows console is not working as expected

Question

I am trying to change the Windows console foreground text color with Rust using the winapi and kernel32 crates.

[dependencies]
winapi = "0.2.8"
kernel32-sys = "0.2.1" 

Code

Enum where I store the foreground color values:

#[repr(u16)]
pub enum ForegroundColor {
    RED =  (winapi::FOREGROUND_INTENSITY | winapi::FOREGROUND_RED) as u16,
    CYAN = (winapi::FOREGROUND_INTENSITY | winapi::FOREGROUND_GREEN | winapi::FOREGROUND_BLUE) as u16,
    // ...
}

Function that gets the output handle:

use winapi;
use winapi::{CONSOLE_SCREEN_BUFFER_INFO, COORD, HANDLE, SMALL_RECT, WORD};
use kernel32;

static mut CONSOLE_OUTPUT_HANDLE: Option<HANDLE> = None;
pub fn get_output_handle() -> HANDLE {
    unsafe {
        if let Some(handle) = CONSOLE_OUTPUT_HANDLE {
            handle_check(handle);
            handle
        } else {
            let handle = kernel32::GetStdHandle(winapi::STD_OUTPUT_HANDLE);
            handle_check(handle);
            CONSOLE_OUTPUT_HANDLE = Some(handle);
            handle
        }
    }
}

fn handle_check(handle: HANDLE) {
    if handle == winapi::INVALID_HANDLE_VALUE {
        panic!("NoConsole")
    }
}

Function that sets the foreground color use kernel32;

// ForegroundColor is a struct containing win32 colors
pub fn set_foreground_color(for_color: ForegroundColor) {
    // function shown above
    let output_handle = kernel::get_output_handle();
    // cast the enum value to a u16: fn to_u16(&self) -> u16 { *self as u16 }
    let forground_color = for_color.to_u16();

    unsafe {
        kernel32::SetConsoleTextAttribute(output_handle, forground_color);
    }
}

In my main.rs I am creating a box that is 20 blocks on X and 20 on Y. I want to give the border a color of CYAN and the inside a RED color.

// for example 1 has to be cyan and 2 red but than on larger scale
// 1111
// 1221
// 1111
for y in 0..21 {
    for x in 0..21 {
        if (x == 0 || y == 0) || (x == 20 || y == 20) {
            // function shown above
            set_foreground_color(ForegroundColor::CYAN);
            // Print a cyan colored ■
            print!("■")
        } else {
            // function shown above
            set_foreground_color(ForegroundColor::RED);
            // Print a red colored ■
            print!("■")
        }
    }
    // reset cursor to start of new line
    println!();
}

For some reason, all ■ will have the CYAN color and there will not be any red ones.

When I have the same code and replace the print!() with println!() , it will print both the RED and CYAN colored blocks as expected. All the ■ have the right color as expected but the problem now is that the ■ are on their own row.

Why is the color of the text changing as expected when using println!() ? Why can I not have different colors on the same line with print!() ? Is there some buffer in winapi that stores the color of the console lines? Do I need to specify it somewhere before I can use multiple colors in one line?

Answer 1

Rust's standard output is line-buffered. So your text gets sent to the console one line at a time, meaning the entire line will have the same color.

You can flush the output after each print! using:

use std::io::Write;

std::io::stdout().flush().expect("Flush stdout failed");