C++ gettid() was not declared in this scope

Question

A simple program is: I would like to get the thread ID of both of the threads using this gettid function. I do not want to do the sysCall directly. I want to use this function.

#include <iostream>
#include <boost/thread/thread.hpp>
#include <boost/date_time/date.hpp>
#include <unistd.h>
#include <sys/types.h>
using namespace boost;
using namespace std;

boost::thread thread_obj;
boost::thread thread_obj1;

void func(void)
{
    char x;
    cout << "enter y to interrupt" << endl;
    cin >> x;
     pid_t tid = gettid();
    cout << "tid:" << tid << endl;
    if (x == 'y') {
        cout << "x = 'y'" << endl;    
        cout << "thread interrupt" << endl;
    }
}

void real_main() {

   cout << "real main thread" << endl;
    pid_t tid = gettid();
    cout << "tid:" << tid << endl;

    boost::system_time const timeout = boost::get_system_time() + boost::posix_time::seconds(3);
    try {
        boost::this_thread::sleep(timeout);
    }
    catch (boost::thread_interrupted &) {
        cout << "thread interrupted" << endl;
    }

}

int main()
{
    thread_obj1 = boost::thread(&func);
    thread_obj = boost::thread(&real_main);
    thread_obj.join();
}

It gives Error on compilation; The use of gettid() has been done according to the man page:

$g++ -std=c++11 -o Intrpt Interrupt.cpp -lboost_system -lboost_thread
Interrupt.cpp: In function ‘void func()’:
Interrupt.cpp:17:25: error: ‘gettid’ was not declared in this scope
      pid_t tid = gettid();

Answer 1

This is a silly glibc bug. Work around it like this:

#include <unistd.h>
#include <sys/syscall.h>
#define gettid() syscall(SYS_gettid)

Answer 2

The man page you refer to can be read online here. It clearly states:

Note: There is no glibc wrapper for this system call; see NOTES.

and

NOTES

Glibc does not provide a wrapper for this system call; call it using syscall(2).

The thread ID returned by this call is not the same thing as a POSIX thread ID (i.e., the opaque value returned by pthread_self(3)).

So you can't. The only way to use this function is through the syscall.

But you probably shouldn't anyway. You can use pthread_self() (and compare using pthread_equal(t1, t2)) instead. It's possible that boost::thread has its own equivalent too.