Update printf value on same line instead of new one

Question

I would like to know if there is a way in C to overwrite an existing value that has already been printed instead of creating a new line every time or just movin

Answer 1

Refer to the sample code to understand:

#include <stdio.h>
#include <pthread.h>

void myThread(void* ptr) {
    printf("Hello in thread\n");
    int i=0;    
    for(;i<10;i++)
    {
        sleep(1);
        printf(". ");
        fflush(stdout);  //comment this, to see the difference in O/P
    }
    printf("sleep over now\n");
}

int main(void) {
    pthread_t tid;
    printf("creating a new thread\n");
    pthread_create(&tid, NULL, (void*)myThread, 0);
    printf("going to join with child thread..\n");
    pthread_join(tid, NULL);
    printf("joined..!!\n");
    return 0;
}

Reference Blog

Answer 2

Have you tested the '\b' character (backspace)? Maybe works depending on your console.

Answer 3

You can do it by using "\r" instead of "\n".

Answer 4

You should add \r to your printf as others have said. Also, make sure you flush stdout, as stdout stream is buffered & will only display what's in the buffer after it reaches a newline.

In your case:

for (int i=0;i<10;i++){
    //...
    printf("\rValue of X is: %d", x/114);
    fflush(stdout);
    //...
}

Answer 5

You can print out as many newlines as the console screen has. This will effectively clear the screen.

This is a great link about clearing screen in different ways.

Answer 6

In addition to answers above, \r is actually a code of the terminal. c seems don't provide a way to change whatever program has already put into stdout stream.

#include<stdio.h>
int main(){
    freopen("output.txt", "w", stdout);
    printf("somthing");
    printf("\r other thing");
}

in output.txt, something doesn't change, cause \r doesn't mean anything for a txt file. But for the terminal, \r is meaningful. It handles format and displays well.

Using terminal codes could do some fun things. like below

#include<iostream>
#include<bits/stdc++.h>
#include<unistd.h>

int main(){
std::string processBar[] {
    "00%: [                     ]",
    "05%: [#                    ]",
    "10%: [##                   ]",
    "15%: [###                  ]",
    "20%: [####                 ]",
    "25%: [#####                ]",
    "30%: [######               ]",
    "35%: [#######              ]",
    "40%: [########             ]",
    "45%: [#########            ]",
    "50%: [##########           ]",
    "55%: [###########          ]",
    "60%: [############         ]",
    "65%: [#############        ]",
    "70%: [##############       ]",
    "75%: [###############      ]",
    "80%: [################     ]",
    "85%: [#################    ]",
    "90%: [###################  ]",
    "95%: [#################### ]",
    "100%:[#####################]",
};

int n = sizeof(processBar)/ sizeof(*processBar);
// pretty fanny
for(int i{0}; i<n; ++i){
    fprintf(stdout, "\e[%d;1H \e[2K \r \a%s", i, processBar[i].c_str());
    fflush(stdout);
    sleep(1);
}

}