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Derived from: BFlattenable
Declared in: be/storage/Path.h
Library: libbe.so
A BPath object represents an absolute pathname, and provides some simple path manipulation and querying functions. The primary features of the class are:
BPaths are handy, but don't expect them to actually do very much: A BPath is just a pathname. It identifies the location of a file, but it can't manipulate the file, nor can it change the structure of the file system.
So what do you use BPaths for?
In the way that they're used, BPaths and entry_refs are nearly identical. In particular, entry_refs can do all three of the things listed here. Whether you use BPaths (pathnames in general) or entry_refs is largely a matter of taste.
You initialize a BPath—in other words, you establish the path that the object represents —by passing a string (or two, or a BDirectory and a string) to the constructor or to the SetTo() function. Upon initialization, the BPath object concatenates the strings and then "normalizes" the passed-in strings if it has to (this emphasis is important, as we'll see in a moment). The following elements trigger normalization:
During normalization, BPath conjures up an absolute pathname in the form
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It does this by applying the following rules:
(The one exception to this final rule is "/" as a full pathname.)
There's a subtle side-effect that you get with normalization: When you normalize a pathname, all the elements in the path up to but not including the leaf must exist. In other words, a normalized BPath object gives you the same guarantee of existence as does an entry_ref structure. The subtlety, here, is that an unnormalized BPath needn't exist at all.
For example, here we create a BPath for a pathname that contains a non-existent directory:
/* We>ll assume that "/abc/def/" doesn't exist. */
BPath path("/abc/def/ghi.jkl");
/* Nonetheless, the BPath is successfully initialized.
* The Path() function returns a pointer to the object>s
* pathname string.
*/
printf("Path: %sn". path.Path());
On the command line we see:
$ Path: /abc/def/ghi.jkl
But if we tickle the normalization machine...
/* The redundant slash causes a normalization. */
BPath path("/abc/def//ghi.jkl");
....the object is invalid:
$ Path: (null)
Both the constructor and the SetTo() function carry an optional argument that lets you force the passed-in path to be normalized:
/* The trailing bool forces normalization. */
BPath path("/abc/def/ghi.jkl", true);
printf("Path: %sn", path.Path());
In this case, the forced normalization nullifies the object:
$Path: (null)
Since forcing normalization makes BPath's behaviour more consistent and reliable, why not always normalize? Because normalization can be expensive.
During normalization, the pathname is stat'd and prodded rather heavily. If you're planning on using your BPath's pathname to initialize a BEntry or BNode, this prodding will happen again. Rather than incur the expense twice, you may want to live with unnormalized BPath objects, and take the normalization hit during the subsequent initialization.
BPath objects are passed back to you (by reference) by a number of Storage Kit functions. However, you shouldn't find any functions that ask for a BPath object. This is a convention of usage:
As an example of a function that returns a BPath to you, recall BEntry's GetPath() function:
status_t BEntry::GetPath(BPath *path)
(As an aside, this is where the auto-allocation comes in handy—because BPath allocates the pathname storage for you, you don't have to mess around with ugly buffer and length arguments.)
On the other hand, BEntry's SetTo() takes a pathname as a const char *:
status_t BEntry::SetTo(const char *path)
If you've got a BPath loaded up with a pathname, you would call this function thus:
entry.SetTo(path.Path());
The constructors and SetTo() functions in (most of) the Storage Kit classes have const char * versions that can be called as shown here.
Let's say you've got a BPath object that you want to send to some other application. To do this, you have to add it to a BMessage object through the latter's AddFlat() function. As an inheritor from BFlattenable, the BPath knows how to flatten itself for just this purpose.
BMessage msg;
BPath path("/boot/lbj/fido");
/* The check here is important, as we>ll describe
* in a moment.
*/
if (msg.AddFlat("pathname", &path) != B_OK)
/* handle the error */
The receiver of the message can retrieve the pathname as a BPath object by calling FindFlat():
void MyApp::MessageReceived(BMessage *msg)
{
BPath path;
if (msg->FindFlat("pathname", &path) != B_OK)
/* handle the error */
...
}
Alternatively, the pathname can be retrieved as an entry_ref through FindRef():
void MyApp::MessageReceived(BMessage *msg)
{
entry_ref ref;
if (msg->FindRef("pathname", &ref) != B_OK)
/* handle the error */
...
}
If you want to skip all the conversion business and simply pass the pathname as a string, use AddString(). The receiver, of course, would have to call FindString() to retrieve your pathname string.
When you add a flattened BPath to a BMessage, the object's pathname is turned into an entry_ref. If the message receiver asks for a BPath (through FindFlat()), the entry_ref is turned back into a BPath object. Therefore, it's more efficient to retrieve a flattened BPath as an entry_ref than it is to unflatten it as a BPath object.
The BPath to entry_ref conversion has another, more subtle implication: Adding a BPath through AddFlat() performs an implicit normalization on the data that's added to the BMessage.
If the normalization fails, the AddFlat() function returns an error and the data isn't added to the BMessage. The original BPath is untouched, regardless of the result of the normalization.
As mentioned earlier, most of the Storage Kit classes have constructors and SetTo() functions that accept const char * arguments. If you want to turn your BPath into a BFile (for example), you would do this (including error checks):
status_t err; BFile file(path.Path()); err = InitCheck();
or
err = file.SetTo(path.Path());
To convert a BPath to an entry_ref, pass the pathname to the get_ref_for_path() function:
entry_ref ref; status_t err; err = get_ref_for_path(path.Path(), &ref);
For you Node Monitor users: You can't convert directly to a node_ref structure. The quickest way from here to there is:
node_ref nref; status_t err; /* We>ll skip InitCheck() and catch errors in GetNodeRef(). */ BEntry entry(path.Path()); err = entry.GetNodeRef(&nref);
Remember, a BPath represents a pathname, not a node. It isn't "updated" when the file system changes:
For example:
BEntry entry;
BPath path;
/* Set a BPath, construct a BEntry from it, rename
* the entry, and then print the BPath>s pathname.
*/
if (path.SetTo("/boot/lbj/fido") == B_OK)
if (entry.SetTo(&path) == B_OK)
if (entry.Rename("rover") == B_OK)
printf("Pathname: %sn", path.Path());
We see...
$ Pathname: /boot/lbj/fido
...even though the entry that the BPath was constructed to represent has been renamed.
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Creates a new BPath object that represents the path that's created from the arguments. See the analogous SetTo() functions for descriptions of the flavorful constructors.
The constructor automatically allocates memory for the object's stored pathname. The memory is freed when the object is deleted.
To check to see if an initialization was successful, call InitCheck().
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Frees the object's pathname storage and extinguishes the object.
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Appends the pathname given by path to the object's current pathname. path must be relative. If normalize is true, the new pathname is normalized; otherwise, it's normalized only if necessary.
Note that this...
Append("subdir/file")
...is the same as (and is implemented as):
path.SetTo(path.Path(), "subdir/file");
The Append() return value is picked up from the SetTo() call.
RETURN CODES
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Initializes the argument with the pathname to the parent directory of this. Destructive parenting is acceptable (sociologically, it's a given):
BPath path("/boot/lbj/fido");
path.GetParent(&path);
Other details...
RETURN CODES
If the initialization isn't successful, the argument's InitCheck() is set to B_NO_INIT.
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Returns the status of the most recent construction or SetTo() call.
RETURN CODES
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These functions return the object's full path and leaf name, respectively. For example:
BPath path("/boot/lbj/fido");
printf("Path: %sn", path.Path());
printf("Leaf: %sn", path.Leaf());
Produces...
$ Path: /boot/lbj/fido $ Leaf: fido
In both cases, the returned pointers belong to the BPath object. When the BPath is deleted, the pointers go with it.
If the BPath isn't initialized, the functions return pointers to NULL.
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The SetTo() function frees the pathname that the object currently holds, and re-initializes the object according to the arguments:
Regarding the leaf argument:
If set to true, the normalize argument tells the object to normalize the new pathname. By default (false), the pathname is normalized only if necessary. Note that the default doesn't mean that the object absolutely won't normalize, it just won't do it if it doesn't think it's necessary. See "Initializing and Normalizing" on page128 for the full story on normalizing a pathname, including the conditions that trigger default normalization. Normalizing has no meaning with the BEntry version of SetTo().
Storage for the pathname is allocated by the BPath object and is freed when the object is deleted (or when you re-initialize through SetTo()). The path and leaf arguments are copied into the allocated storage.
Other details...
/* This works... */ path.SetTo(path.Path(), ...);
Unset() frees the object's pathname storage and sets the InitCheck() value to B_NO_INIT.
RETURN CODES
The return value is also recorded in InitCheck().
The following functions are implemented in accordance with the rules set down by the BFlattenable class. You never need to invoke these functions directly; they're implemented so a BPath can added to a BMessage (see "Passing a BPath in a BMessage" on page130). But in case you're interested...
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Returns true if code is B_REF_TYPE, and false otherwise.
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Converts the object's pathname to an entry_ref and writes it into buffer. Currently, size is ignored.
RETURN CODES
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Returns the size of the entry_ref that represents the flattened pathname.
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Returns false.
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Returns B_REF_TYPE.
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Initializes the BPath with the flattened entry_ref data that's found in buffer. The type code must be B_REF_TYPE.
RETURN CODES
The Unflatten() return value is recorded in InitCheck().
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Initializes this with a copy of the pathname that's gotten from the argument. Also sets InitCheck().
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Compares this's pathname with the pathname taken from the argument. The comparison is a simple strcmp(); neither path is normalized or otherwise altered before the comparison is made. For example:
BPath path("/boot/lbj/fido");
chdir("/boot");
printf("Are they equal? %dn", path == "lbj/fido");
Displays:
$ Are they equal? 0
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