Scanf function is ignored in Docker

Asked May 06 '22 at 07:47

Active May 06 '22 at 08:06

Viewed 34 times

I am using docker to test my C code if it works in ubuntu. I tested my code with clang and gcc in Mac-os, it works and i used VirtualBox to test in Ubuntu too, it works as well, but in docker i don't know why but scanf() ignored every time. I doesn't cause any error but it just ignores and go on the rest of code.

This my test code

int main(int argc, char** argv)
{
    printf("... main running ...\n");
    
    int a;
    scanf("%d", &a);
    printf("%d", a);

    return 0;
}

edited May 06 '22 at 08:06

asked May 06 '22 at 07:47

cacarekt

You've created a 5-line program testing this? Just echoing what you read? Can you post that? – MSalters May 06 '22 at 07:50
Please take some time to refresh [the help pages](http://stackoverflow.com/help), take the SO [tour], read [ask], as well as [this question checklist](https://codeblog.jonskeet.uk/2012/11/24/stack-overflow-question-checklist/). And please don't forget how to create a **[mre]** to show us, or how to [edit] your questions. – Some programmer dude May 06 '22 at 07:50
@MSalters i edited the post, can you check again – cacarekt May 06 '22 at 08:06
1

I suggest you flush the output buffer either by adding a `\n` newline or with `fflush(stdout)`. – Weather Vane May 06 '22 at 08:07
1

Check what `scanf` [*returns*](https://en.cppreference.com/w/cpp/io/c/fscanf#Return_value). And what is the input you give your program? How do you give this input? – Some programmer dude May 06 '22 at 08:07
@Someprogrammerdude it returns -1 in docker – cacarekt May 06 '22 at 08:09
That means you have an error. If you get an error use `perror("scanf failed")` to print a message. What does it tell you? – Some programmer dude May 06 '22 at 08:11
@Someprogrammerdude it doesn’t tell anything, it just ignores and continue the rest of code. – cacarekt May 06 '22 at 08:15
I mean something like `if (scanf(...) == -1) { perror("scanf failed"); }`. What is the output from that? – Some programmer dude May 06 '22 at 08:17
How do you start it in docker? – bdecaf May 06 '22 at 08:17
it says `scanf failed: Success` – cacarekt May 06 '22 at 08:19
@bdecaf with DockerFile – cacarekt May 06 '22 at 08:19
I think it is something with Docker, maybe Docker just doesn't allow to input types – cacarekt May 06 '22 at 08:23
You probably need to start it interactive. Try following https://stackoverflow.com/questions/59965032/docker-run-with-interactive-and-tty-flag – bdecaf May 06 '22 at 08:27
Feel free to post a self answer. Others might find it useful. – bdecaf May 06 '22 at 08:36

Scanf function is ignored in Docker

0 Answers0