Is it possible to print out (in C) a line of text to the console on a Linux OS containing a variable so that when the variable changes, it changes the printed line instead of printing a new line? For example, if I have the following C code:
void main()
{
int i;
for(i=1;i<=10;i++){
printf("%d\n",i);
sleep(5);
}
}
As is, that would print ten lines. But I want to print one line that updates itself to show the value of i when it changes.
On Linux, void main(void) is undefined behaviour; the return type is int — no exceptions. On Windows, the rules are different; on Unix, they're simple — main() returns int!
Use '\r' carriage return and fflush():
#include <stdio.h>
int main(void)
{
int i;
for (i = 1; i <= 10; i++)
{
printf("\r%d", i);
fflush(stdout);
sleep(5);
}
putchar('\n');
return 0;
}
No need to use the curses library unless your display needs get more complex.
Note: if you are counting down (or the length of the current row of output decreases for any reason), you need to make sure you write blanks over previously displayed data. So, for example, you might need the format string "\r%-4d" to count from 9999 to 0 without leaving unwanted digits on display.
Something like the following should do the job (taken / modified from How to update a printed message in terminal without reprinting (Linux))
int main(int argc, char *argv[]) {
for(int i=1;i<=10;++i) {
printf("\r[%3d%%]",i);
fflush(0);
sleep(5);
}
printf("\n");
}
Not exactly sure what you are up to, but maybe writing the content of your variable into a temporary file and using watch(1) to visualize it is an option?
