为了测试获取线程id，所以用

#include <unistd.h>
pid_t tid = gettid();
cout << "now pid is:" << tid << endl;

但是每次编译都会报错：

[root@localhost cpp]# g++ test.cpp -o test  -lpthread
test.cpp: 在函数‘void* say_hello(void*)’中:
test.cpp:16:20: 错误：‘gettid’在此作用域中尚未声明
pid_t tid = gettid();
解决办法：

加入以下，

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

贴完整测试代码：

#include <iostream>

#include <ctime>
#include <cstdlib>
#include <pthread.h>
#include <unistd.h>
#include <sys/syscall.h>
#define gettid() syscall(SYS_gettid)
using namespace std;

#define NUM_THREADS 5

void* say_hello(void* args)
{
cout << "Hello Runoob！" << endl;

pid_t tid = gettid();
cout << "now pid is:" << tid << endl;
return 0;
}
int main()
{

pthread_t tids[NUM_THREADS];
for (int i = 0; i < NUM_THREADS; ++i)
{

int ret = pthread_create(&tids[i], NULL, say_hello, NULL);
if (ret != 0)
{
cout << "pthread_create error: error_code=" << ret << endl;

}
else
{
cout << "tids:" << tids[i] << endl;
}
}

pthread_exit(NULL);
cin.get();
return 0;
}

为了测试获取线程id，所以用#include &amp;lt;unistd.h&amp;gt;pid_t tid = gettid(); cout &amp;lt;&amp;lt; &quot;now pid is:&quot; &amp;lt;&amp;lt; tid &amp;lt;&amp;lt; endl; 但是每次编译都会报错：[root@localhost cpp]# g++ test.cpp -o test  -lpthreadtest.cpp: ... cd /usr/local/src wget https://cdn.mysql.com//Downloads/MySQL-8.0/mysql-boost-8.0. 20 .tar.gz wget https://cmake.org/files/v3.12/cmake-3.12.0-rc1.tar.gz yum install -y gcc gcc- c++ make automake cmake ncurses ncurses-devel