Related Info: File Manager (PBxxx)

XCMD Corner: Catalog XCMD

By Donald Koscheka, Arthur Young & Co., MacTutor Contributing Editor

Bullet Proofing

Recently, Joe Palooka wrote to complain about a bug in the GetFileName XCMD that appeared in this column a few months back. Apparently, the xcmd bombed if you passed it more than four file types. But this letter raises a more important issue: how much bulletproofing should I do to my code examples?

Before you jump to the obvious conclusion, allow me to make my case. Bulletproofing my code examples carries three liabilities for this column, size and clarity and time. The former is obvious. This magazine can carry only a certain number of pages per issue. Exceeding that page limit on a regular basis will result in my column getting bumped or serialized. I would like to avoid either case.

Clarity is not so obvious and, in fact, is a function of size. The larger a program is, the more unreadable it becomes. Bulletproofing code tends to be fairly routine, and one can almost apply a formula to XCMDs for bulletproofing: (1) Are the input parameters defined? (2) if so, are they properly conditioned (e.g. correct number of data).

The final liability is time. My years of experience have taught me that a large amount of a programming project’s time is spent anticipating exceptions. Working under a monthly deadline, it is often necessary to eliminate this step. I don’t see any contradiction here. If you intend to use my code in your own product, then it’s incumbent on you test its effectiveness. Bulletproofing my examples will only make your job harder and even then, I have no way of anticipating your exceptions (i.e. what happens to subroutine x if I make this small change to its parameters?)

This code tends to take the form:

if( paramPtr->params[i] && **(paramPtr->params[i]) )...

Testing the input parameters is something else entirely and can easily exceed the size of the “functional code”.

This is not to belittle the need for bulletproof code. Far from it. If you intend to use the code in this column, you should use it as a starting point. In general, if you intend to use somebody else’s code, you should seek answers to these questions: what does the code do? what doesn’t the code do?

At any rate, I will leave this issue on your hands. Write to the editor and let him know your feelings.

Catalog

One good XCMD deserves another. Recently, Joe Zuffoletto called me to ask whether I had any intentions of writing an XCMD that returns a catalog of a given directory. You may recall that Joe gave us the series on adding standard Mac windows to Hypercard. Such code cannot go unrewarded and so this month’s xcmd ...

Catalog accepts parameters in one of two forms. If you pass a pathname in the first parameter, it will return a catalog of all files in that directory. If the first parameter is empty, then Catalog will use the second parameter as directory reference number. This second parameter requires further explaining by way of the file manager.

When the user selects a file from the standard file dialog, the name as well as the volume reference number is passed back to the caller. Under HFS, the volume reference number masquerades as a working directory id. In reality, this reference number acts as either a volume reference number or a working directory id. How the file manager tells them apart is subtle but important:

Volume reference numbers are small negative integers such as -1, -2, -3... In fact, if you pass such a number to Catalog, you will get a listing of the root directory of the volume in question.

Working directory id’s are x. Working directories must not be confused with directory id’s. Each file has a unique id assigned to it called a directory id. This id is a long integer that uniquely identifies a file or folder. Working directory id’s by contrast are integers and are not unique for a given folder. Working directories are very much like file reference numbers. When a working directory is opened by the call, PBOpenWD, a reference number is returned in the vRefNum field.

Listing 1:

/********************************/
/* File: Catalog.c */
/* */
/* Given the reference number of*/
/* a working directory or volume*/
/* return a list of all files & */
/* folders in that directory*/
/* */
/* if a name is given, use it,*/
/* otherwise, use the id passed  */
/********************************/

#include<MacTypes.h>
#include<OSUtil.h>
#include<MemoryMgr.h>
#include<FileMgr.h>
#include<ResourceMgr.h>
#include<pascal.h>
#include<string.h>
#include<hfs.h>
#include  “HyperXCmd.h”
#include“HyperUtils.h”

#define nil 0L

extern  GetCatalog();

pascal void main( paramPtr )
 XCmdBlockPtr  paramPtr;
{
 Handle catalog;
 Str31  str;
 short  dirID;

 /*** intialize the output container ***/
 catalog = NewHandle( 0L );
 
 /*** convert the wdid to a usable form            ***/
 if( paramPtr->params[1] ){
 HLock( paramPtr->params[1] );
 ZeroToPas( paramPtr, *(paramPtr->params[1]), &str );
 HUnlock( paramPtr->params[1] );
 dirID = (short)StrToNum( paramPtr, &str );

 /*** given the id of a directory, ***/
 /*** return a catalog for that directory ***/
 GetCatalog( dirID, catalog );
 }
 else if( paramPtr->params[0] ){ 
 char   path[256];
 CInfoPBRec catPB;
 WDPBRecwdPB;
 
 HLock( paramPtr->params[0] );
 ZeroToPas( paramPtr, *(paramPtr->params[0]), &path );
 HUnlock( paramPtr->params[0] );
 
 /*** get a directory id to this path***/          
 catPB.dirInfo.ioNamePtr  = (StringPtr)path;
 catPB.dirInfo.ioFDirIndex  = 0;
 catPB.dirInfo.ioVRefNum  = 0;
 if( PBGetCatInfo( &catPB, 0 ) == noErr )
   if( catPB.dirInfo.ioFlAttrib & 0x010 ){   /*** it’s a directory
 ***/
 wdPB.ioNamePtr  = (StringPtr)path; 
   wdPB.ioWDProcID = 0;
  
 if( PBOpenWD( &wdPB, 0 ) == noErr ){
 wdPB.ioWDVRefNum= catPB.dirInfo.ioVRefNum;
 wdPB.ioWDDirID  = catPB.dirInfo.ioDrDirID;
 GetCatalog( wdPB.ioVRefNum, catalog );
 PBCloseWD( &wdPB, 0 );
 }
   }
 }
 /*** append a null to the end of the***/
 /*** the directory for Hypercard  ***/
 AppendCharToHandle( catalog, ‘\0’ );
 
 paramPtr->returnValue = catalog;
}

Listing 2:

#include<MacTypes.h>
#include<OSUtil.h>
#include<MemoryMgr.h>
#include<FileMgr.h>
#include<ResourceMgr.h>
#include<pascal.h>
#include<hfs.h>
#include<string.h>
#include  “HyperXCmd.h”
#include“HyperUtils.h”

/*** If you read this column***/
/*** column on a regular basis***/
/*** you may want to add these***/
/*** routines to HyperUtils.c ***/
/*** If you don’t have Hyper- ***/
/*** utils.c, you can obtain it  ***/
/*** from MacTutor for a small***/
/*** handling charge ***/

#define SYNC0

AppendCharToHandle( theHand, theChar )
 Handle theHand;
 char theChar;
/****************************
* Given a valid handle, append
* the character passed in to 
* the end of the handle
* 
* This is a useful way to embed
* \r, \t or \0 into a container
* for use by hypercard.
****************************/
{
 long   hsiz = GetHandleSize( theHand );
 char   *dirP;

 SetHandleSize( theHand, hsiz + 1 );
 dirP = *theHand + hsiz;
 *dirP= theChar;
}

GetCatalog( wdref, dirH )
 short  wdref;
 Handle dirH;
/****************************
* Get a listing of the directory
* passed in.
* In:
*  wdref == reference number of the
*  the desired working directory
*dirH == handle to the output container.
* Note that we allocate all structures 
* in the heap to minimize the impact
* a high directory valence might have
* on the stack.
****************************/
{
 OSErr  done= 0; /* goes true when done searching  */
 CInfoPBPtr catPB= (CInfoPBPtr)NewPtr( sizeof(CInfoPBRec));
 WDPBPtrwdPB= (WDPBPtr)NewPtr( sizeof(WDPBRec));
 char   *fname = (char *)NewPtr( 256L );

 if( catPB && wdPB && fname ){
 catPB->dirInfo.ioNamePtr = (StringPtr)fname;
 catPB->dirInfo.ioFDirIndex = 0;
 catPB->dirInfo.ioVRefNum = wdref; 
 
 do{
 *(catPB->dirInfo.ioNamePtr) = ‘\0’;
 catPB->dirInfo.ioFDirIndex++;
 catPB->dirInfo.ioDrDirID = 0; 
 
 if( (done = PBGetCatInfo( catPB, SYNC ) ) == noErr ){
 pStrToField( fname, ‘’, dirH );
   if( catPB->dirInfo.ioFlAttrib & 0x010 ){  /*** it’s a directory
 ***/
 AppendCharToHandle( dirH, ‘:’ );
   }
   AppendCharToHandle( dirH, ‘\r’ );
 }
 }while( !done );
 
 DisposPtr( (Ptr)catPB );
 DisposPtr( (Ptr)wdPB );
 DisposPtr( (Ptr)fname );
 }
}