How to do terminal loading effect on just one line?

Question

How can I do a loading effect by refreshing a terminal line when running a program in c?

Example:

carrying...

points are increasing.

I can do this effect in a while loop but just cleaning the screen with the command

system("clear");

I would just like to update a line.

Answer 1

You can print a CR (\r, Carriage Return, which returns the cursor to the beginning of the line), clear the line and then continue printing its points, as in the example below:

#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
#include <time.h>

void main() {
    printf("Hello world\n");
    for (int i = 0; i < 10; i++) {
        printf("Carregando %d", i);
        for (int j = 0; j < 40; j++) {
            printf(".");
            Sleep(20);
        }
        printf("\r");
        for (int j = 0; j < 60; j++) {
            printf(" "); // apaga a linha anterior
        }
        printf("\r");
    }
    printf("\nGoodbye\n");
}

Answer 2

If you are using Linux (as seems to be the case given your attempt to call clear), an interesting solution* is to use the X-Term commands to clear the screen and move the cursor to row 0 and column 0. For example:

#include <stdio.h>

void cls(void)
{
    printf("\033[2J");   // Limpa a tela
    printf("\033[0;0H"); // Devolve o cursor para a linha 0, coluna 0
}

int main(void)
{
    printf("Esta é uma linha de texto\n");
    cls();
    printf("Esta é uma nova linha de texto\n");
    return 0;
}

If your idea is just to "animate" a loading message, instead of clearing the screen it is more practical and fast to simply move the cursor back to the home column. Here’s an example that animates the dots:

#include <stdio.h>
#include <signal.h>
#include <sys/time.h>

int dots = 1;
void reset();
unsigned int alarm();
void animation(int signo);


int main(void)
{
    printf("\n\n\n\n      Carregando");
    signal(SIGALRM, animation);
    alarm(1);

    while(1)
        getchar();

    return 0;
}

void reset(void)
{
    printf("\033[10D");         /* Move 10 colunas para a esquerda */
    printf("          ");       /* Imprime 10 espaços em branco */
    printf("\033[10D");         /* Move 10 colunas para a esquerda */
}

unsigned int alarm (unsigned int seconds)
{
    struct itimerval old, new;
    new.it_interval.tv_usec = 0;
    new.it_interval.tv_sec = 0;
    new.it_value.tv_usec = 0;
    new.it_value.tv_sec = (long int) seconds;
    if (setitimer (ITIMER_REAL, &new, &old) < 0)
        return 0;
    else
        return old.it_value.tv_sec;
}

void animation(int signo)
{
    signal(SIGALRM, animation);
    alarm(1);

    (void)(signo); /* apenas ignora o parâmetro */

    printf(".");
    dots++;
    if(dots > 10)
    {
        dots = 1;
        reset();
    }
}

Note that this solution does not work on Windows. If you want to use something more standardized to emulate your own terminal, worth evaluating the ncurses (which also has a port for Windows).

^{* My answer was created with help of this SOEN response.}

Answer 3

I appreciate the answers but it didn’t work with me, I use linux, I tried to adapt, but still the result didn’t come out as intended.

I got it fixed, I adapted it from this code and the @carlosfigueira code, analyzing the link code you can see that there is a problem in it as i increases.

So I had to understand the workings of a printf, the \r and only in this way could I formulate a solution.

The solution is this:

  #include <stdio.h>
  #include <time.h>

  void limpa_linha(void);

  int main (int argc, char **argv){    
     int i, j;

     system ("clear");//limpa tela
     printf ("\n\nCarregando: \n\n");          

     for (i = 0; i <= 100; i++){             
        printf ("%d%%  ", i);      
        fflush (stdout);//garante a escrita de dados imediatamente na tela                  
        //repare mod 10, eu limito a qtd de pontos q serao gerados
        for (j = 0; j < i%10; j++){
           printf(".");
        }  
        fflush (stdout);//garante a escrita de dados imediatamente na tela
        usleep(500000);//função espera por tempo, parametro em microsegundos.
        limpa_linha();                    
     }                 
     printf ("\n\n Fim\n\n");            
     return 0;
  }

  void limpa_linha(){
     int i;//indice do caracter na linha
     int max_caracter=50;//indica o maximo de caracter que a linha pode chegar a ter, para linhas com mt texto, coloque um nmr bem maior
     printf("\r");//retorna para o inicio da linha que pretende reutilizar, isso não limpa a linha, apenas posiciona cursor ao inicio da linha

     //Agora precisamos limpar a linha,
     //substitui todos os caracteres existentes por espaço em branco
     for(i=0;i<max_caracter;i++){
        printf(" ");//vai preenchendo a linha com espaços em branco
     }

     printf("\r");//volta ao inicio da linha , dessa vez ela está em branco.

  }