%\pagebreak
\section{\kcode{target enter data} and \kcode{target exit data} Constructs}
\label{sec:target_enter_exit_data}
%\section{Simple target enter data and target exit data Constructs}
\index{constructs!target enter data@\kcode{target enter data}}
\index{constructs!target exit data@\kcode{target exit data}}
\index{target enter data construct@\kcode{target enter data} construct}
\index{target exit data construct@\kcode{target exit data} construct}

The structured data construct (\kcode{target data}) provides persistent data on a
device for subsequent \kcode{target} constructs as shown in the 
\kcode{target data} examples above. This is accomplished by creating a single
\kcode{target data} region containing \kcode{target} constructs.

The unstructured data constructs allow the creation and deletion of data on
the device at any appropriate point within the host code, as shown below 
with the \kcode{target enter data} and \kcode{target exit data} constructs.

\index{map clause@\kcode{map} clause!alloc map-type@\kcode{alloc} map-type}
\index{map clause@\kcode{map} clause!delete map-type@\kcode{delete} map-type}
\index{alloc map-type@\kcode{alloc} map-type}
\index{delete map-type@\kcode{delete} map-type}
The following C++ code creates/deletes a vector in a constructor/destructor 
of a class. The constructor creates a vector with \kcode{target enter data}
and uses an \kcode{alloc} modifier in the \kcode{map} clause to avoid copying values
to the device. The destructor deletes the data (\kcode{target exit data})
and uses the \kcode{delete} modifier in the \kcode{map} clause to avoid copying data
back to the host. Note, the stand-alone \kcode{target enter data} occurs 
after the host vector is created, and the \kcode{target exit data}
construct occurs before the host data is deleted.

\cppexample[4.5]{target_unstructured_data}{1}

%\pagebreak
The following C code allocates and frees the data member of a \ucode{Matrix} structure.
The \ucode{init_matrix} function allocates the memory used in the structure and
uses the \kcode{target enter data} directive to map it to the target device. The
\ucode{free_matrix} function removes the mapped array from the target device
and then frees the memory on the host.  Note, the stand-alone 
\kcode{target enter data} occurs after the host memory is allocated, and the 
\kcode{target exit data} construct occurs before the host data is freed.

\cexample[4.5]{target_unstructured_data}{1}

%\pagebreak
The following Fortran code allocates and deallocates a module array, \ucode{A}.  The
\ucode{initialize} subroutine allocates the module array and uses the
\kcode{target enter data} directive to map it to the target device. The
\ucode{finalize} subroutine removes the mapped array from the target device and
then deallocates the array on the host.  Note, the stand-alone 
\kcode{target enter data} occurs after the host memory is allocated, and the 
\kcode{target exit data} construct occurs before the host data is deallocated.

\ffreeexample[4.5]{target_unstructured_data}{1}
%end