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Re: 20010103: multi-dimensional array writes in c++

>To: address@hidden
>cc: address@hidden
>From: Bill Cassanova <address@hidden>
>Subject: multi-dimensional array writes in c++
>Organization: UCAR/Unidata
>Keywords: 200201031845.g03IgdN17359

Hi Bill,

> I am using the netCDF c++ interface and have not been able to find
> an example of doing a multi-dimensional put.
> 
> Here's a couple of code snippets.
> 
> First the CDL:
> netcdf foo{
> dimensions:
>    msn = 18000 ;
>    ftd = 1 ;
>    fvd = 10 ;
> variables:
>    int site_list(msn) ;
>    float maxt_f(msn, fvd) ;
>    float mint_f(msn, fvd) ;
>    int icon_code1(msn, fvd) ;
> };
> 
> Now the C++ portion:
> float foo[10][10];
> for( int i = 0; i < 10; i++ ){
>       for( int j = 0; j < 10; j++ ){
>               foo[i][j] = 999;
>       }
> }
> 
> NcVar *var=nc->get_var( "maxt_f" );
> assert(var);
> var->put( foo, 10, 10 );
> 
> The problem is the netCDF interface requires a float * instead of a
> float **.  Is there some way other than allocating another float * 
> and copying foo into it to make this work?
> 
> I've tried:
> var->put((int*)*foo, 10, 10 );
> var->put(*foo[0], 10, 10 );

Try

  var->put(&foo[0][0], var->edges());

or equivalently

  var->put(foo[0], var->edges());

There's an example that puts data in a 3-dimensional array in the
distributed netCDF source in the file

 src/cxx/example.cpp

which is supposed to do the same thing in C++ that the equivalent C
code does in

 src/cxx/example.c

Generally in either C or C++, if the prototype of a function requires
a foo* argument (a pointer to a foo), then you can supply a &foo (the
address of a foo).  Since the netCDF C++ interface requires a float*
and foo[0][0] is a float, then &foo[0][0] is a float* so is the right
type.  You could also use just foo[0], since a diagram of how arrays
work in C (or C++) shows that's the same as &foo[0][0].

Please let us know if this doesn't work.

--Russ