[ROOT] sizeof(Long_t)

From: Robert Hatcher (rhatcher@SLAC.stanford.edu)
Date: Sat Nov 04 2000 - 02:23:06 MET 

I'm confused about the sizeof Long_t.  I'm running ROOT:
  *   Version   2.25/03 15 September 2000   *
and g++ gives:
  Reading specs from /usr/lib/gcc-lib/i386-redhat-linux/egcs-2.91.66/specs
  gcc version egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)

In Rtypes.h there is code:

#ifdef R__B64
typedef int            Seek_t;      //File pointer
typedef long           Long_t;      //Signed long integer 4 bytes
typedef unsigned long  ULong_t;     //Unsigned long integer 4 bytes
#else
typedef int            Seek_t;      //File pointer
typedef long           Long_t;      //Signed long integer 8 bytes
typedef unsigned long  ULong_t;     //Unsigned long integer 8 bytes
#endif

Here Long_t is always typedef'd to "long" even when long isn't 8 bytes.
The only difference between these two parts is the comments.  I thought
Long_t was intended to be a uniform size (8 bytes) in a platform 
independent manner -- just like Int_t is 4 bytes even when "int" isn't.
But even if it isn't the comments are exactly backwards;  R__B64
*isn't* defined for this platform so the second block is the relevant one.
But there the comments say one should expect a 8 byte Long_t when it isn't.

-robert

Robert W. Hatcher   |  rhatcher@slac.stanford.edu
Research Associate  |  650.926.3171  [FAX 4001 or 3587]
Stanford University |  PO Box 4349, MS #63, Stanford CA 94309

============ test_sizeof.C ======================
#ifndef  __CINT__
#include <iostream.h>
#endif

void test_sizeof()
{

#ifdef R__B64
  cout << "R__B64 is defined " << endl;
#else
  cout << "R__B64 is not defined " << endl;
#endif
  cout << "sizeof(char)      " << sizeof(char)      << endl;
  cout << "sizeof(Char_t)    " << sizeof(Char_t)    << endl;
  cout << "sizeof(short)     " << sizeof(short)     << endl;
  cout << "sizeof(Short_t)   " << sizeof(Short_t)   << endl;
  cout << "sizeof(int)       " << sizeof(int)       << endl;
  cout << "sizeof(Int_t)     " << sizeof(Int_t)     << endl;
  cout << "sizeof(long)      " << sizeof(long)      << endl;
  cout << "sizeof(Long_t)    " << sizeof(Long_t)    << endl;
  cout << "sizeof(float)     " << sizeof(float)     << endl;
  cout << "sizeof(Float_t)   " << sizeof(Float_t)   << endl;
  cout << "sizeof(double)    " << sizeof(double)    << endl;
  cout << "sizeof(Double_t)  " << sizeof(Double_t)  << endl;
#ifndef  __CINT__
  cout << "sizeof(long long) " << sizeof(long long) << endl;
#else
  cout << "CINT doesn't recognize 'long long' by default " << endl;
#endif
}

This archive was generated by hypermail 2b29 : Tue Jan 02 2001 - 11:50:36 MET