DESCRIPTION
A Column contains an ordered sequence of data. The data in a single Column should all be of a single type.
DfcColumn is actually a proxy class in order to make the complexity of the implementation details less obvious to the user.
CAUTIONS

EXAMPLES

    DfcColumn mycol = myTable.getColumn(2); 
  
  try 
  { 
        for (int loop = 0; loop < mycol.getNumRows(); loop++) 
    { 
      cout << myCol.DELETEME(loop) << endl;  
    } 
  } 
  catch(DfcTypeExc e) 
  { 
    cerr << "Column does not hold scalar values\n"; 
  } 

          {
    myTable.select(myTable.getColumn("observer") == "bob");
  }
  catch (DfcTypeExc e)
  {
    cerr << "Column doesn't contain string data\n";
  }
  try
  {
    for (int loop = 0; loop < myCol.getNumRows(); loop++)
    {
      if (myTable.isRowSelected(loop))
      {
        cout << myCol.DELETEME(loop) << endl;
      }
    }
  }
  catch(DfcTypeExc e)
  {
    cerr << "Column does not hold scalar values\n";
  }
  
    try
  {
    DfcCoordSysInterfaceZPA coordObject = myColumn.getAsCoordSys();
                    DfcCoordSysInterfaceTAN tanProjection = myColumn.getAsCoordSys();
  } 
  catch(DfcTypeExce e) 
  { 
    cerr << "Column doesn't contain DfcCoordSysInterface objects\n"; 
  } 
  

DESIGN DECISIONS
DfcColumn contains a fat interface, meaning all the methods of all subclasses are defined whether they are relevant or not. For example we have get() methods for every type of Column that can exist. Of course, this may not be possible in some cases. For example if we have a Column of integers and we invoke getAsCoord(). This method will then throw an exception. This is not an ideal situation as it probably means a LOT of code for checking types or, if a lazy programmer starts to use it, very unsafe code. However, there is no way around it given the requirements - the nature of the objects is not service oriented, it is data oriented.
One nice touch that minimises the concern over types is by allowing conversions where possible between types. For example, if we have a Column that contains Time objects, we can disregard the actual type of Time object by conerting between them and providing the user with whatever type they require. See the examples for more info.
Unfortunately now that we are not dealing with parameterised types explicitly through the use of proxy classes as in the previous design, there is a need to make all the operators explicit in the base class. It can be seen that there are a horrific number of operators now, a set for each type of Column.
Various compromises have been attempted in the course of this rewoek of the design for example, only access methods are provided in this class. To access the rest of the functionality the user must cast down to the appropriate type. Then a proxy class should be reintroduced to make the casting safe. Then we are dealing with template classes again, which was frowned upon. So I would have to create inmstantiations ofthe proxy class - basically just typedef it. Then the user has to use the Info class and the data class again like in the previous design. However, in my mind this seperation doesn't stand up any more when data can be accessed from the base class, it doesn't make sense to have to downcast in the hierarchy in order to be able to access certain methods. So I have completely abandoned this idea and instead opted for the full set of methods in the base class. The implications of this are:
1 - the interface is very large as can be seen. This makes it difficult to find a method that you suspect should be there.
2 - maintenance is therefore harder, even though the methods are very simple, the organisational aspect of the classes is more difficult especially if we ever wish to add in more Column types.
3 - exceptions will have to be generated when the user attempts to use inappropriately typed methods for a class eg if we select all rows where the contents of the row is less than 5, but the contents are actually Frame References. There's either going to be a lot of exception processing (and the current iplementation of exceptions in g++ seems dodgy) or there's going to be a lot of non-OO switch-on-type style code written by the users.

Also it should be noted that for scalar types it is not possible to do transparent overloading because of the following problem: eg
DFC_BOOL operator<(float value) const;
DFC_BOOL operator<(double value) const;
..because if we port to an architecture where 64 bit reals are not supported we would have to make double a 32 bit real ie the same as float which then means the code won't compile as we are trying to declare a method twice.
Therefore all operators involving scalar data will be done to double precision only which may lead to some ugly casting in the user code.

Exceptions

• DfcMemoryExc - there wasn't enough memory on the local machine to make a copy.
• DfcAlreadyOpenExc - the Column is already opened for update and therefore a copy can't be made.

Arguments

Exceptions

• DfcMemoryExc - there wasn't enough memory on the local machine to make a copy.
• DfcAlreadyOpenExc - the Column is already opened for update and therefore a copy can't be made.

Arguments

Exceptions

• DfcMemoryExc - there wasn't enough memory to create this column with the desired space.

Arguments

Exceptions

• DfcMemoryExc - there wasn't enough memory to create this column with the desired space.
• DfcInvalidExpExc - the provided expression was not valid.

Arguments

Returns
The dimensions of the structure. Rather than raise an exception if something non-numeric is being accessed (ie a KeywordStructure, or a Column of Frames, the Dimensions returned will be zero.

Exceptions

• DfcTypeExc - the actual data contained in the Column is such that it does not make sense to have a null value that is a double.

Arguments

Returns
The current representation of the Null value.

Exceptions

• DfcTypeExc - it is not possible to express the type of the Column as a double.

Returns
A Boolean stating whether the Null value representation has been set or not.

Returns
Status of the Column, selected or not.

Returns
Returns a copy of the name of the Column. Actually copies the name rather than returning a reference in order to make sure we don't have any dangling pointers or references later.

Exceptions

• DfcAlreadyExistsExc - this Column is part of a table and the new name already exists in that table. If this exception is raised then the name of the Column stays as it was.

Arguments

Returns
Returns an indication of the type of data that is held in the Columns.

Arguments

• value - the value to compare each entry in the column against.

Returns
A vector of booleans. The length of this vector is the same as the Column. Each entry in the vector indicates whether the corresponding entry in the Column passed the comparison or not.

Exceptions

• DfcTypeExc - the type presented as an argument cannot be compared against the actual type of the Column.

Arguments

• value - the integer value to compare each entry in the column against.

Returns
A vector of booleans. The length of this vector is the same as the Column. Each entry in the vector indicates whether the corresponding entry in the Column passed the comparison or not.

Exceptions

• DfcTypeExc - the type presented as an argument cannot be compared against the actual type of the Column.

Arguments

• value - the integer value to compare each entry in the column against.

Returns
A vector of booleans. The length of this vector is the same as the Column. Each entry in the vector indicates whether the corresponding entry in the Column passed the comparison or not.

Exceptions

• DfcTypeExc - the type presented as an argument cannot be compared against the actual type of the Column.

Arguments

• value - the integer value to compare each entry in the column against.

Returns
A vector of booleans. The length of this vector is the same as the Column. Each entry in the vector indicates whether the corresponding entry in the Column passed the comparison or not.

Exceptions

• DfcTypeExc - the type presented as an argument cannot be compared against the actual type of the Column.

Arguments

• value - the integer value to compare each entry in the column against.

Returns
A vector of booleans. The length of this vector is the same as the Column. Each entry in the vector indicates whether the corresponding entry in the Column passed the comparison or not.

Exceptions

• DfcTypeExc - the type presented as an argument cannot be compared against the actual type of the Column.

Arguments

• value - the integer value to compare each entry in the column against.

Returns
A vector of booleans. The length of this vector is the same as the Column. Each entry in the vector indicates whether the corresponding entry in the Column passed the comparison or not.

Exceptions

• DfcTypeExc - the type presented as an argument cannot be compared against the actual type of the Column.

Returns
A double value.

Exceptions

• DfcTypeExc - Could not convert the value to an int, for example maybe we're dealing with a Column of Coordinate Systems.
• DfcBoundsExc - the supplied positionVector specified a point outside the bounds of the container object we're using eg we're looking at a column of 30 elements and tried to access element number 50.
• DfcDimensionsExc - the position vector had the wrong number of elements in it to specify a point. For example, we're examining a Column and supplied a position Vector that did not have exactly one element in it.

Arguments

Returns
An int value.

Exceptions

• DfcTypeExc - Could not convert the value to an int, for example maybe we're dealing with a Column of Coordinate Systems.
• DfcBoundsExc - the supplied positionVector specified a point outside the bounds of the container object we're using eg we're looking at a column of 30 elements and tried to access element number 50.
• DfcDimensionsExc - the position vector had the wrong number of elements in it to specify a point. For example, we're examining a Column and supplied a position Vector that did not have exactly one element in it.

Arguments

Exceptions

• DfcTypeExc - Could not convert the value to an int, for example maybe we're dealing with a Column of Coordinate Systems.
• DfcBoundsExc - the supplied positionVector specified a point outside the bounds of the container object we're using eg we're looking at a column of 30 elements and tried to access element number 50.
• DfcDimensionsExc - the position vector had the wrong number of elements in it to specify a point. For example, we're examining a Column and supplied a position Vector that did not have exactly one element in it.

Arguments

Exceptions

• DfcTypeExc - Could not convert the value to an int, for example maybe we're dealing with a Column of Coordinate Systems.
• DfcBoundsExc - the supplied positionVector specified a point outside the bounds of the container object we're using eg we're looking at a column of 30 elements and tried to access element number 50.
• DfcDimensionsExc - the position vector had the wrong number of elements in it to specify a point. For example, we're examining a Column and supplied a position Vector that did not have exactly one element in it.

Arguments

{large Returns}
A copy of the top level Keyword associated with the Column. This object is a proxy so it doesn't make any diference whether it is treated as a reference or a copy of it is made, both will still alter the Keywords structure. (A reference is not returned beacuse, although it slightly reduces the amount of work to be done, it increases the risk of memory leaks by transferring responsibility of the referenced object to the user.)

Returns
A pointer to the copy of this object. The responsibility for the memory management of this copy now lies with the method invoker.

Exceptions

• DfcMemoryExc - there was not enough memory on the local machine to perform the copy succesfully.
• DfcAlreadyOpenExc - the original is opened for update. There can only be one copy of a Column open for update at any one time, therefore the clone() operation has to fail.

Arguments

Returns
Reference to this object to allow chaining of assignment operators.

Exceptions

• DfcAlreadyOpenExc - the original is opened for update. There can only be one copy of a Column open for update at any one time, therefore the clone() operation has to fail.

Preconditions
A column with the same name as this object exists.

Returns
DFC_BOOL - indicating whether this object has been populated with data or not. Possible reasons for failure is that a Column with the same name as this object does not exist, or that the Column is already opened for update.

Exceptions

• DfcDoesntExistExc - attempted to open a Column with a name that does not exist.
• DfcAlreadyOpenExc - the Column is already open. In this case it has been opened for update by somebody else.

Preconditions
The Column is not currently being used anywhere else. It has not been opened for read or for update.

Returns
Boolean indication of whether the open succeeded or not.Possible reasons for failure is that a Column with the same name as this object does not exist, or that the Column is already opened for update, or for read somewhere else.

Exceptions

• DfcDoesntExistExc - there is no column existing with the name given.
• DfcAlreadyOpenExc - the Column is currently open for reading or updating somewhere else.

Preconditions
The Table that this Column is associated with has been opened for update, not for read.

Returns
DFC_BOOL - an indication of whether the save succeded or not.

Exceptions

• DfcReadOnlyExc - an attempt was made to save a Column belonging to a Table that was not opened for update. Opening a Table for read does not disable the possibility of changing the local copy, but the changes cannot be saved back to the Image Repository.

Returns
A pointer to a DfcKeyword object