Re: What is the maximum acceptable size of an array?

Hi John,
sure it is related to stack size. When it is not compiled, then this array created by new. If you will do instead of
  char a[MAX];
char *a = new char[MAX];
and at the end delete [] a
it will work allways correctly
Victor

 Victor M. Perevoztchikov perev_at_bnl.gov Brookhaven National Laboratory MS 510A PO Box 5000 Upton NY 11973-5000 tel office : 631-344-7894; fax 631-344-4206;

• Original Message ----- From: John Zoidberg To: roottalk_at_root.cern.ch Sent: Monday, July 09, 2007 12:02 PM Subject: [ROOT] What is the maximum acceptable size of an array?

  I've encountered a strange problem in one of my macros. I managed to reduce it to an array size problem.

  This macro runs without errors when compiled (.L toto.C+) with "#define MAX 1972432" and exits root without any message if compiled with "#define MAX 1972433":
//includes

  #include <iostream>
  using namespace std;

//OK

  #define MAX 1972432
//not OK
//#define MAX 1972433

//main function

  int toto()
  {
    char a[MAX];     

    cout<<"MAX="<<MAX<<endl;
    cout<<"total size="<<MAX*sizeof(char)<<" bytes"<<endl;
    cout<<"total size="<<(float)MAX*(float)sizeof(char)/1024.<<" Kilobytes"<<endl;
    cout<<"total size="<<(float)MAX*(float)sizeof(char)/(1024.*1024.)<<" Megabytes"<<endl;
    cout<<"total size="<<MAX*sizeof(char)*8<<" bits"<<endl;
    

    return(0);
  }

  You might have to change the limit values of MAX to see this problem on your PC.   I noticed that it's quite random sometimes. Sometimes it worked with 1972432 and sometimes not.   I also recommend quitting and restarting ROOT after each test because it seems to always work if you stay in the ROOT shell even after recompiling.

  Other tests I made:

  This macro runs without error when not compiled (.x toto2.C):
//includes

  #include <iostream>
  using namespace std;

//OK

  #define MAX 10000000
//not OK
//#define MAX 1972433

//main function

  int toto2()
  {
    char a[MAX];     

    cout<<"MAX="<<MAX<<endl;
    cout<<"total size="<<MAX*sizeof(char)<<" bytes"<<endl;
    cout<<"total size="<<(float)MAX*(float)sizeof(char)/1024.<<" Kilobytes"<<endl;
    cout<<"total size="<<(float)MAX*(float)sizeof(char)/(1024.*1024.)<<" Megabytes"<<endl;
    cout<<"total size="<<MAX*sizeof(char)*8<<" bits"<<endl;
    

    return(0);
  }

  This C++ program compiles and runs without error:
//includes

  #include <iostream>
  using namespace std;

//OK

  #define MAX 10000000
//not OK
//#define MAX 1972433

//main function

  int main()
  {
    char a[MAX];     

    cout<<"MAX="<<MAX<<endl;
    cout<<"total size="<<MAX*sizeof(char)<<" bytes"<<endl;
    cout<<"total size="<<(float)MAX*(float)sizeof(char)/1024.<<" Kilobytes"<<endl;
    cout<<"total size="<<(float)MAX*(float)sizeof(char)/(1024.*1024.)<<" Megabytes"<<endl;
    cout<<"total size="<<MAX*sizeof(char)*8<<" bits"<<endl;
    

    return(0);
  }

  So, is there any rational explanation to this?   Should I use TCloneArrays or TNtuples instead? Received on Mon Jul 09 2007 - 18:30:54 CEST