Error: An integer constant expression is required within the array subscrip

Question

hello all,
here is a small piece of code which compile well with g++:
#include <iostream>
using namespace std;
int main () {
int i= 0, j=4 ;
cout <<" i=" ; cin >> i ;
cout  << "i="<<i<< endl;
if ( i > 1) {
   double xx [i+5];
   int n= i+5;
   for (int k =0 ; k < n ; k++) xx[k] =k;
  cout << "xx[2]=" << xx[2] << " xx[4]=" << xx[4] <<" xx["<<i<<"]="<< xx[i] <<en
dl;
  cout << "xx[1]=" << xx[3] << " xx[5]=" << xx[4] <<" xx["<<n-1<<"]="<< xx[n-1]
<<endl;
}with Sun Studio 12 CC, the error is:
"x.C", line 12: Error: An integer constant expression is required within the array subscript operator.
1 Error(s) detected.Is there an option to force CC to accept it? i read that CC has some gnu extensions (http://docs.sun.com/source/820-4155/c++.html)
Thanks in advance for help,
gerard

Answer 1

This works:
#include <iostream>
#include <alloca.h>
using namespace std;
int main () {
int i= 0, j=4 ;
cout <<" i=" ; cin >> i ;
cout  << "i="<<i<< endl;
if ( i > 1) {
   double *xx = ( double * ) alloca( sizeof( *xx ) * ( i + 5 ) );
   int n= i+5;
   for (int k =0 ; k < n ; k++) xx[k] =k;
  cout << "xx[2]=" << xx[2] << " xx[4]=" << xx[4] <<" xx["<<i<<"]="<< xx[i] <<en
dl;
  cout << "xx[1]=" << xx[3] << " xx[5]=" << xx[4] <<" xx["<<n-1<<"]="<< xx[n-1]
<<endl;
}