ArcGIS Engine Developer Guide

C++ APPLICATION PROGRAMMING INTERFACE
For further details on GUIDs, see ‘The Microsoft
Component Object Model’ section earlier in this
chapter.
IUID
There are several methods in ArcObjects that take an IUID object as a parameter.
An IUID object is a globally unique identifier object. It can be either a GUID, as
shown in the example below, or a ProgID.
IUIDPtr ipUID(CLSID_UID);
IEnumLayerPtr ipEnumLayer;
// Use IGeoFeatureLayer's GUID.
hr = ipUID->put_Value(CComVariant(L"{E156D7E5-22AF-11D3-9F99-
00C04F6BC78E}"));
hr = ipMap->get_Layers(ipUID, VARIANT_TRUE, &ipEnumLayer);
You might notice that the samples and scenarios
do not follow the Good Error Handling practices
outlined here. This is done simply to increase
code readability since error checking is not the
focus of those bits of code.
ERROR HANDLING
COM methods return an HRESULT to signify the success or failure of a call, as
discussed in the ‘Developing with ArcObjects’ section earlier in this chapter.
When you are programming with the C++ API, you should check the returned
HRESULT of all calls to COM objects.
There are a few common HRESULTs that can be returned.
• S_OK signifies success.
• E_FAIL indicates a failure.
• E_NOTIMPL indicates a method is not implemented.
There are some macros that can be used to test the returned HRESULT.
• bool FAILED(HRESULT)
For example, if the opening of a workspace in which you want to process
data fails, you will not be able to use the data. At that point, you should exit
the application to avoid a crash later.
// Open the workspace.
IWorkspaceFactoryPtr ipWorkspaceFactory(CLSID_RasterWorkspaceFactory);
IWorkspacePtr ipWorkspace;
HRESULT hr = ipWorkspaceFactory->OpenFromFile(inPath, 0, &ipWorkspace);
if (FAILED(hr) || ipWorkspace == 0)
{
std::cerr