ANSI转义码ESC [0E未能按预期工作

Question

I was trying out the example code from this answer .

#include <iostream>
#include <thread>
#include <chrono>

void drawProgressBar(int, double);

int main() {

    drawProgressBar(30, .25);
    std::this_thread::sleep_for(std::chrono::seconds(1));
    drawProgressBar(30, .50);
    std::this_thread::sleep_for(std::chrono::seconds(1));
    drawProgressBar(30, .75);
    std::this_thread::sleep_for(std::chrono::seconds(1));
    drawProgressBar(30, 1);

    return 0;
}

void drawProgressBar(int len, double percent) {
    std::cout << "\x1B[2K"; // Erase the entire current line.
    std::cout << "\x1B[0E"; // Move to the beginning of the current line.
    std::string progress;
    for (int i = 0; i < len; ++i) {
        if (i < static_cast<int>(len * percent)) {
            progress += "=";
        } else {
            progress += " ";
        }
    }
    std::cout << "[" << progress << "] " << (static_cast<int>(100 * percent)) << "%" << std::flush;
}

The expected behavior was a progress bar like so:

[=======                       ] 25%

which would update three times on the same line, ending up as:

[==============================] 100%

after 3 seconds.

While each progress bar gets erased as expected, the next progress bar is drawn one line down, not on the same line as I was expecting it to.

The documentation linked in the answer ( Wikipedia ) says that CSI n E ( ESC[nE ) where n is an integer:

Moves cursor to beginning of the line n (default 1) lines down.

So I would expect CSI 0 E ( ESC[0E ) to move the cursor to the beginning of the current line (the line 0 lines down).

Why doesn't it? Also, how can I achieve the intended behavior?

---

I'm using Terminal.app on OS X to run this program.

Answer 1

Hmm, try:

std::cout << "\r";

instead of:

std::cout << "\x1B[2K"; // Erase the entire current line.
std::cout << "\x1B[0E"; // Move to the beginning of the current line.

This is a carriage return , which should reposition the cursor at the beginning of the line.

(By the way, kudos for commenting your code. Love it when people do that on here :) )