how to get thread id of a pthread in linux c program?

Question

In linux c program, how to print thread id of a thread created by pthread library?
for ex: we can get pid of a process by getpid()

Answer 1

As noted in other answers, pthreads does not define a platform-independent way to retrieve an integral thread ID.

On Linux systems, you can get thread ID thus:

#include 
pid_t tid = gettid();

On many BSD-based platforms, this answer https://stackoverflow.com/a/21206357/316487 gives a non-portable way.

However, if the reason you think you need a thread ID is to know whether you're running on the same or different thread to another thread you control, you might find some utility in this approach

static pthread_t threadA;

// On thread A...
threadA = pthread_self();

// On thread B...
pthread_t threadB = pthread_self();
if (pthread_equal(threadA, threadB)) printf("Thread B is same as thread A.\n");
else printf("Thread B is NOT same as thread A.\n");

If you just need to know if you're on the main thread, there are additional ways, documented in answers to this question how can I tell if pthread_self is the main (first) thread in the process?.