CODEWITHSUNDEEP
clinuxsigint
ardabro
ardabro

Reputation: 2061

SIGINT lost when output redirected; how to detect termination in program?

I wrote console program that detects SIGINT, so when user press Ctrl+C program performs some actions and terminates.

But when I redirect this program with pipe to any other, for example: ./my_program | tee xxx SIGINT never comes to my handler. Despite this program terminates. Handing SIGTERM gives no effects. SIGTERM does not come after Ctrl+C too.

How can I detect that program is aborted by Ctrl+c in all situations?

My test case with SIGINT and SIGPIPE:

    #include <csignal>
#include <cstdio>

bool break_request=false;
bool term_request=false;

extern "C" void break_handler(int)
{
    break_request=true;
    printf("Ctrl+C detected\n");
}

extern "C" void term_handler(int)
{
    term_request=true;
    printf("pipe detected\n");
}

int main()
{
    signal(SIGINT,break_handler);
    signal(SIGPIPE,term_handler);

    while(true)
    {
        if(break_request)
        {
            printf("break request handled\n");
            break;
        }

        if(term_request)
        {
            printf("pipe request handled\n");
            break;
        }
    }

    printf("terminating\n");
}

Upvotes: 2

Views: 1128

Answers (2)

William Morris
William Morris

Reputation: 3684

Your printf output is going down the pipe. Use fprintf(stderr, "...") instead.

Upvotes: 3

Dietrich Epp
Dietrich Epp

Reputation: 213758

If your program is used in a pipe, it will get SIGPIPE if it writes when there's no reader on the other side.

Just install a SIGPIPE handler.

Upvotes: 0

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