对"omp_get_num_procs"的未定义引用

# include <cstdlib>
# include <iostream>
# include <iomanip>
# include <omp.h>
using namespace std;
int main ( int argc, char *argv[] );
//********************************
int main ( int argc, char *argv[] )
//**********************************
{
  int id;
  double wtime;
  cout << "n";
  cout << "HELLO_OPENMPn";
  cout << "  C++/OpenMP versionn";
  cout << "n";
  cout << "  Number of processors available = " << omp_get_num_procs ( ) << "n";
  cout << "  Number of threads =              " << omp_get_max_threads ( ) << "n";
  wtime = omp_get_wtime ( );
# pragma omp parallel 
  private ( id )
  {
    id = omp_get_thread_num ( );
    cout << "  This is process " << id << "n";
  }
  wtime = omp_get_wtime ( ) - wtime;
  cout << "n";
  cout << "HELLO_OPENMPn";
  cout << "  Normal end of execution.n";
  cout << "n";
  cout << "  Elapsed wall clock time = " << wtime << "n";
  return 0;
}

你好我尝试运行这个程序：

我运行"文件名"，出现此错误：

G++ hello_openmp.cpp -o hello_openmp/tmp/ccz80Tfg.o：在函数main': hello_openmp.cpp:(.text+0x4d): undefined reference to omp_get_num_procs'hello_openmp.cpp：（.text+0x7a）：未定义对omp_get_max_threads' hello_openmp.cpp:(.text+0xa7): undefined reference to omp_get_wtime的引用hello_openmp.cpp：（.text+0xb9）：未定义对omp_get_thread_num' hello_openmp.cpp:(.text+0xea): undefined reference to omp_get_wtime的引用collect2：错误：ld 返回 1 个退出状态生成： *** [hello_openmp] 错误 1

有谁知道这个错误的含义是什么。对不起，我是C++初学者。谢谢