RWDBNullIndicator Class Reference

Provides a way to determine whether some given data is NULL. More...

#include <rw/db/nullind.h>

Public Member Functions
	RWDBNullIndicator (bool value=0)
	operator bool () const

Detailed Description

RWDBNullIndicator allows application code:

• to determine whether a particular piece of data extracted from an RWDBReader is NULL
• to specify whether a bound value is NULL when using an RWDBBoundExpr

An RWDBNullIndicator instance may be interpreted as a boolean value: true means a data item is NULL; false means a data item is not NULL.

Synopsis

#include <rw/db/nullind.h>
 
RWDBNullIndicator nullInd;

See also

RWDBNullIndicator is designed specifically to detect NULL values as they are extracted from an RWDBReader. See RWDBReader for more details.

The setting of RWDBDatabase::emptyStringIsNull can affect the way that empty strings are inserted and read. For more details, see RWDBManager::emptyStringIsNull(bool).

Example

This code fragment selects an integer and a string from a table, and checks for NULL before processing the results:

RWDBTable myTable = myDBase.table("myTable");
RWDBSelector select = myDBase.selector();
select << myTable["id"] << myTable["name"];
RWDBReader rdr = select.reader();
int id;
RWCString name;
RWDBNullIndicator idIsNull;
RWDBNullIndicator nameIsNull;
 
while (rdr()) {
  rdr >> idIsNull >> id >> nameIsNull >> name;
  if (idIsNull || nameIsNull) {
    // handle NULL case
  } else {
    // process name and id normally
  }
}

Constructor & Destructor Documentation

RWDBNullIndicator()

RWDBNullIndicator::RWDBNullIndicator ( bool value = 0 )

inline

Constructs an RWDBNullIndicator with the given initial value.

Member Function Documentation

operator bool()

RWDBNullIndicator::operator bool ( ) const

inline

Returns the current boolean value of self.