All Databases Inside Mac - Basic Toolbox

ReadPartialResource

Get a handle to part of a resource

#include <Resources.h> Resource Manager

void ReadPartialResource(theResource, offset, buffer, count);

Handle theResource ; 4-byte ResType; resource type to get

long offset ; start of section to be obtained

Ptr buffer ; buffer to contain the partial resource

long count ; length of section

You can use the ReadPartialResource and WritePartialResource

procedures to manipulate a subsection of a large, unwieldy resource that may

not otherwise fit in memory. You can use the SetResourceSize procedure to

change the size of a resource on disk to a size that you specify.

Be aware that having a copy of a resource in memory when you are using the

partial resource routines may cause problems. If you have modified the copy in

memory and then access the resource on disk using either the

ReadPartialResource or WritePartialResource procedure, you will

lose changes made to the copy in memory.

The ReadPartialResource procedure reads part of a resource in from disk,

which allows you to work with small portions of large resources. This

procedure reads into memory a section of the resource, which is specified by

the parameter theResource. The value of the offset parameter marks the

beginning of the subsection as measured in bytes from the start of the

resource. The length of the section is given by the value of the count parameter.

The ReadPartialResource procedure reads the partial resource into the

buffer you indicate with the buffer parameter. You are responsible for the

memory management of this buffer. You cannot use the ReleaseResource

procedure to release the memory occupied by this buffer. Call the ResError

function to check for errors.

The ReadPartialResource procedure always tries to read resources from

the disk. If a resource is already in memory, the Resource Manager still

reads it from the disk and ResError returns the resourceInMemory result

code. If you have loaded the resource into memory and modified it, you will lose

any changes to the resource once you call the ReadPartialResource

procedure. If you try to read past the end of a resource or your offset is out of

bounds, ResError returns the inputOutOfBounds error. If the handle named

by the parameter theResource is not in any open resource files, ResError

returns the resNotFound result code.

When using partial resource routines, you should call the SetResLoad

procedure specifying FALSE for its load parameter before you call the

GetResource function. SetResLoad prevents the Resource Manager from

reading the entire resource into memory. Be sure to restore the normal state

of the SetResLoad procedure after you call the GetResource function.

Note: If the resource is in memory and you want part of its data, you

should use the BlockMove procedure instead of the

ReadPartialResource procedure, because BlockMove is faster.

Returns: an Error Code. It will be one of:

resourceInMemory (-188) Resource already in memory

inputOutOfBounds (-190) Offset or count out of bounds

resNotFound (-192) Resource not found

Referenced by (4):