==============.L f2.cxx=========================
void f2(int n, double *x)
{
for(int i=0;i<100;i++){
  x[i]=3.5+i*12.356;
}
n = 10;
return;
}
//
void f2a(int &n, double *x)
{
for(int i=0;i<100;i++){
  x[i]=3.5+i*12.356;
}
n = 10;
return;
}
//
void f2b(int &n, double &x)
{
for(int i=0;i<100;i++){
  x[i]=3.5+i*12.356;
}
n = 10;
return;
}

================.x f2.C===================================-
{
//test external function-----
// .L f2.cxx  before doing .x f1.C
double x[500];
int n=3;
//
cout<<"----f2(int n, double* x)-----"<<endl;
f2(n, x);
cout<<"n= "<<n<<endl;
for (int i=0;i<n;i++){
  cout<<i<<" x[i]= "<<x[i]<<endl;
}
//
cout<<"----f2a(int &n, double* x)-----"<<endl;
f2a(n, x);
cout<<"n= "<<n<<endl;
for (int i=0;i<n;i++){
  cout<<i<<" x[i]= "<<x[i]<<endl;
}
//
cout<<"----f2b(int &n, double& x)-----"<<endl;
f2b(n, x);
cout<<"n= "<<n<<endl;
for (int i=0;i<n;i++){
  cout<<i<<" x[i]= "<<x[i]<<endl;
}


===============results===================================
root [19] .x f2.C
----f2(int n, double* x)-----
n= 3
0 x[i]= 3.5
1 x[i]= 15.856
2 x[i]= 28.212
----f2a(int &n, double* x)-----
n= 10
0 x[i]= 3.5
1 x[i]= 15.856
2 x[i]= 28.212
3 x[i]= 40.568
4 x[i]= 52.924
5 x[i]= 65.28
6 x[i]= 77.636
7 x[i]= 89.992
8 x[i]= 102.348
9 x[i]= 114.704
----f2b(int &n, double& x)-----
Error: Function f2b(n,x) is not defined in current scope  f2.C:20:
*** Interpreter error recovered ***