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KeySet :: Class Methods

KeySet :: Class Methods

Section: C Library Functions (3) Updated: Tue Nov 2 2010
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NAME

KeySet :: Class Methods -

Methods to manipulate KeySets.

 

Functions


KeySet * ksNew (size_t alloc,...)

KeySet * ksDup (const KeySet *source)

int ksCopy (KeySet *dest, const KeySet *source)

int ksDel (KeySet *ks)

void ksSort (KeySet *ks)

ssize_t ksGetSize (const KeySet *ks)

ssize_t ksAppendKey (KeySet *ks, Key *toAppend)

ssize_t ksAppend (KeySet *ks, const KeySet *toAppend)

Key * ksPop (KeySet *ks)

int ksRewind (KeySet *ks)

Key * ksNext (KeySet *ks)

Key * ksCurrent (const KeySet *ks)

Key * ksHead (const KeySet *ks)

Key * ksTail (const KeySet *ks)

cursor_t ksGetCursor (const KeySet *ks)

int ksSetCursor (KeySet *ks, cursor_t cursor)

Key * ksLookup (KeySet *ks, Key *key, option_t options)

Key * ksLookupByName (KeySet *ks, const char *name, option_t options)
 

Detailed Description

Methods to manipulate KeySets.

A KeySet is a unsorted set of keys.

Terminate with ksNew(0) or ksNew(20, ..., KS_END) This is because there is a list of Key* required and KS_END has the length of (Key*).

It can be implemented in various ways like a linked list or with a dynamically allocated array.

With ksNew() you can create a new KeySet.

You can add keys with ksAppendKey() in the keyset. ksGetSize() tells you the current size of the keyset.

With ksRewind() and ksNext() you can navigate through the keyset. Don't expect any particular order, but it is assured that you will get every key of the set.

KeySets have an internal cursor . This is used for ksLookup() and kdbSet().

KeySet has a fundamental meaning inside elektra. It makes it possible to get and store many keys at once inside the database. In addition to that the class can be used as high level datastructure in applications. With ksLookupByName() it is possible to fetch easily specific keys out of the list of keys.

You can easily create and iterate keys:

#include <kdb.h>

// create a new keyset with 3 keys
// with a hint that about 20 keys will be inside
KeySet *myConfig = ksNew(20,
        keyNew ('user/name1', 0),
        keyNew ('user/name2', 0),
        keyNew ('user/name3', 0),
        KS_END);
// append a key in the keyset
ksAppendKey(myConfig, keyNew('user/name4', 0));

Key *current;
ksRewind(myConfig);
while ((current=ksNext(myConfig))!=0) {
        printf('Key name is %s., keyName (current));
}
ksDel (myConfig); // delete keyset and all keys appended


   

Function Documentation

 

ssize_t ksAppend (KeySet * ks, const KeySet * toAppend)Append all toAppend contained keys to the end of the ks.

toAppend KeySet will be left unchanged.

Makes the keyset dirty, see ksSort().

Returns:

the size of the KeySet after transfer

-1 on NULL pointers

Parameters:

ks the KeySet that will receive the keys
toAppend the KeySet that provides the keys that will be transfered

See also:

ksAppendKey(), ksInsert(), ksInsertKeys()

 

ssize_t ksAppendKey (KeySet * ks, Key * toAppend)Appends a Key to the end of ks.

A pointer to the key will be stored, and not a private copy. So a future ksDel() on ks may keyDel() the toAppend object, see keyGetRef().

The reference counter of the key will be incremented, and thus toAppend is not const.

The KeySet internal cursor is not moved.

Makes the keyset dirty, see ksSort().

Returns:

the size of the KeySet after insertion

-1 on NULL pointers

Parameters:

ks KeySet that will receive the key
toAppend Key that will be appended to ks

See also:

ksInsert(), ksInsertKeys(), ksAppend(), keyNew(), ksDel()

keyIncRef()

 

int ksCopy (KeySet * dest, const KeySet * source)Copy a keyset.

Most often you may want a duplicate of a keyset, see ksDup() or append keys, see ksAppend(). But in some situations you need to copy a keyset to a existing keyset, for that this function exists.

You can also use it to clear a keyset when you pass a NULL pointer as source.

Note that all keys in dest will be deleted. Afterwards the content of the source will be added to the destination and the ksCurrent() is set properly in dest.

A flat copy is made, so the keys will not be duplicated, but there reference counter is updated, so both keysets need to be ksDel().

int f (KeySet *ks)
{
        KeySet *c = ksNew (20, ..., KS_END);
        // c receives keys
        ksCopy (ks, c); // pass the keyset to the caller

        ksDel (c);
}       // caller needs to ksDel (ks)

Parameters:

source has to be an initialized source KeySet or NULL
dest has to be an initialized KeySet where to write the keys

Returns:

1 on success

0 if dest was cleared successfully (source is NULL)

-1 on NULL pointer

See also:

ksNew(), ksDel(), ksDup()

keyCopy() for copying keys

 

Key* ksCurrent (const KeySet * ks)Return the current Key.

The pointer is NULL if you reached the end or after ksRewind().

Note:

You must not delete the key or change the key, use ksPop() if you want to delete it.

Parameters:

ks the keyset object to work with

Returns:

pointer to the Key pointed by ks's cursor

0 on NULL pointer

See also:

ksNext(), ksRewind()

kdbMonitorKeys() for a usage example

 

int ksDel (KeySet * ks)A destructor for KeySet objects.

Cleans all internal dynamic attributes, decrement all reference pointers to all keys and then keyDel() all contained Keys, and free()s the release the KeySet object memory (that was previously allocated by ksNew()).

Parameters:

ks the keyset object to work with

Returns:

0 when the keyset was freed

-1 on null pointer

See also:

ksNew()

 

KeySet* ksDup (const KeySet * source)Return a duplicate of a keyset.

Objects created with ksDup() must be destroyed with ksDel().

Memory will be allocated as needed for dynamic properties, so you need to ksDel() the returned pointer.

A flat copy is made, so the keys will not be duplicated, but there reference counter is updated, so both keysets need ksDel().

Parameters:

source has to be an initializised source KeySet

Returns:

a flat copy of source on success

0 on NULL pointer

See also:

ksNew(), ksDel()

keyDup() for Key :: Basic Methods duplication

 

cursor_t ksGetCursor (const KeySet * ks)Get the KeySet internal cursor.

Use it to get the cursor of the actual position.

Warning:

Cursors are getting invalid when the key was ksPop()ed or ksLookup() with KDB_O_POP was used.

 

Read ahead

With the cursors it is possible to read ahead in a keyset:

cursor_t jump;
ksRewind (ks);
while ((key = keyNext (ks))!=0)
{
        // now mark this key
        jump = ksGetCursor(ks);

        //code..
        keyNext (ks); // now browse on
        // use ksCurrent(ks) to check the keys
        //code..

        // jump back to the position marked before
        ksSetCursor(ks, jump);
}

 

Restoring state

It can also be used to restore the state of a keyset in a function

int f (KeySet *ks)
{
        cursor_t state = ksGetCursor(ks);

        // work with keyset

        // now bring the keyset to the state before
        ksSetCursor (ks, state);
}

It is of course possible to make the KeySet const and cast its const away to set the cursor. Another way to achieve the same is to ksDup() the keyset, but it is not as efficient.

An invalid cursor will be returned directly after ksRewind(). When you set an invalid cursor ksCurrent() is 0 and ksNext() == ksHead().

Note:

Only use a cursor for the same keyset which it was made for.

Parameters:

ks the keyset object to work with

Returns:

a valid cursor on success

an invalid cursor on NULL pointer or after ksRewind()

See also:

ksNext(), ksSetCursor()

 

ssize_t ksGetSize (const KeySet * ks)Return the number of keys that ks contains.

Parameters:

ks the keyset object to work with

Returns:

the number of keys that ks contains.

-1 on NULL pointer

See also:

ksNew(0), ksDel()

 

Key* ksHead (const KeySet * ks)Return the first key in the KeySet.

The KeySets cursor will not be effected.

If ksCurrent()==ksHead() you know you are on the first key.

Parameters:

ks the keyset object to work with

Returns:

the first Key of a keyset

0 on NULL pointer or empty keyset

See also:

ksTail() for the last Key :: Basic Methods

ksRewind(), ksCurrent() and ksNext() for iterating over the KeySet :: Class Methods

 

Key* ksLookup (KeySet * ks, Key * key, option_t options)Look for a Key contained in ks that matches the name of the key.

 

Introduction

ksLookup() is designed to let you work with entirely pre-loaded KeySets, so instead of kdbGetKey(), key by key, the idea is to fully kdbGet() for your application root key and process it all at once with ksLookup().

This function is very efficient by using binary search. Together with kdbGet() which can you load the whole configuration with only some communication to backends you can write very effective but short code for configuration.  

Usage

If found, ks internal cursor will be positioned in the matched key (also accessible by ksCurrent()), and a pointer to the Key is returned. If not found, ks internal cursor will not move, and a NULL pointer is returned.

Cascading is done if the first character is a /. This leads to ignoring the prefix like system/ and user/.

        if (kdbGet(handle, 'user/myapp', myConfig, 0 ) == -1)
                ErrorHandler ('Could not get Keys');

        if (kdbGet(handle, 'system/myapp', myConfig, 0 ) == -1)
                ErrorHandler ('Could not get Keys');

        if ((myKey = ksLookup(myConfig, key, 0)) == NULL)
                ErrorHandler ('Could not Lookup Key');

This is the way multi user Programs should get there configuration and search after the values. It is guaranteed that more namespaces can be added easily and that all values can be set by admin and user.  

KDB_O_NOALL

When KDB_O_NOALL is set the keyset will be only searched from ksCurrent() to ksTail(). You need to ksRewind() the keyset yourself. ksCurrent() is always set properly after searching a key, so you can go on searching another key after the found key.

When KDB_O_NOALL is not set the cursor will stay untouched and all keys are considered. A much more efficient binary search will be used then.

So if you change keys, e.g. rename (keySetName()) or remove (keyRemove()) them make sure to sort the keyset with ksSort(). When the keyset is dirty, see ksNeedSort() it will be sorted automatically when needed.  

KDB_O_POP

When KDB_O_POP is set the key which was found will be ksPop()ed. ksCurrent() will not be changed, only iff ksCurrent() is the searched key, then the keyset will be ksRewind()ed.

Note:

Note that keyRemove() keys won't be found after the first time the keyset is resorted. Lookup automatically sorts the keyset, if needed, but it can't find it out when only keys are changed, not the keyset.

Like in ksPop() the popped key always needs to be keyDel() afterwards, even if it is appended to another keyset.

Warning:

All cursors on the keyset will be invalid iff you use KDB_O_POP, so don't use this if you rely on a cursor, see ksGetCursor().

Note:

Never use ksLookup() with KDB_O_POP and ksAppendKey() or ksAppend() together in a loop. Otherwise ksLookup() will need to resort the keyset every iteration and spend 99.96% of the time in ksSort() (benchmarked with above 500k iterations).

You can solve this problem by using KDB_O_NOALL, risking you have to iterate n^2 instead of n.

The more elegant way is to separate the keyset you use for ksLookup() and ksAppendKey():

int f(KeySet *iterator, KeySet *lookup)
{
        KeySet *append = ksNew (ksGetSize(lookup), KS_END);
        Key *key;
        Key *current;

        ksRewind(iterator);
        while (current=ksNext(iterator))
        {
                key = ksLookup (lookup, current, KDB_O_POP);
                // do something...
                ksAppendKey(append, key); // now append it to append, not lookup!
                keyDel (key); // make sure to ALWAYS delete poped keys.
        }
        ksAppend(lookup, append);
        // now lookup needs to be sorted only once, append never
        ksDel (append);
}

Parameters:

ks where to look for
key the key object you are looking for
options some KDB_O_* option bits:
KDB_O_NOCASE

 Lookup ignoring case.
KDB_O_WITHOWNER

 Also consider correct owner.
KDB_O_NOALL

 Only search from ksCurrent() to end of keyset, see above text.
KDB_O_POP

 Pop the key which was found.
KDB_O_SORT

 Force sorting before searching, see ksSort(). Together with KDB_O_NOALL the search will start from beginning. 

Returns:

pointer to the Key found, 0 otherwise

0 on NULL pointers

See also:

ksLookupByName() to search by a name given by a string

ksCurrent(), ksRewind(), ksNext() for iterating over a KeySet :: Class Methods

ksSort() to understand how KeySet :: Class Methods sort themself

 

Key* ksLookupByName (KeySet * ks, const char * name, option_t options)Look for a Key contained in ks that matches name.

ksLookupByName() is designed to let you work with entirely pre-loaded KeySets, so instead of kdbGetKey(), key by key, the idea is to fully kdbGetByName() for your application root key and process it all at once with ksLookupByName().

This function is very efficient by using binary search. Together with kdbGetByName() which can you load the whole configuration with only some communication to backends you can write very effective but short code for configuration.

If found, ks internal cursor will be positioned in the matched key (also accessible by ksCurrent()), and a pointer to the Key is returned. If not found, ks internal cursor will not move, and a NULL pointer is returned.  

Cascading

Cascading is done if the first character is a /. This leads to ignoring the prefix like system/ and user/.

        if (kdbGetByName(handle, '/sw/myapp/current', myConfig, 0 ) == -1)
                ErrorHandler ('Could not get Keys');

        if ((myKey = ksLookupByName (myConfig, '/myapp/current/key', 0)) == NULL)
                ErrorHandler ('Could not Lookup Key');

This is the way multi user Programs should get there configuration and search after the values. It is guaranteed that more namespaces can be added easily and that all values can be set by admin and user.  

Full Search

When KDB_O_NOALL is set the keyset will be only searched from ksCurrent() to ksTail(). You need to ksRewind() the keyset yourself. ksCurrent() is always set properly after searching a key, so you can go on searching another key after the found key.

When KDB_O_NOALL is not set the cursor will stay untouched and all keys are considered. A much more efficient binary search will be used then.

Parameters:

ks where to look for
name key name you are looking for
options some KDB_O_* option bits:
KDB_O_NOCASE

 Lookup ignoring case.
KDB_O_WITHOWNER

 Also consider correct owner.
KDB_O_NOALL

 Only search from ksCurrent() to end of keyset, see above text.
KDB_O_POP

 Pop the key which was found.
KDB_O_SORT

 Force sorting before searching, see ksSort(). Together with KDB_O_NOALL the search will start from beginning.

Currently no options supported.

Returns:

pointer to the Key found, 0 otherwise

0 on NULL pointers

See also:

keyCompare() for very powerful Key lookups in KeySets

ksCurrent(), ksRewind(), ksNext()

 

KeySet* ksNew (size_t alloc, ...)Allocate, initialize and return a new KeySet object.

Objects created with ksNew() must be destroyed with ksDel().

You can use a various long list of parameters to preload the keyset with a list of keys. Either your first and only parameter is 0 or your last parameter must be KEY_END.

For most uses

KeySet *keys = ksNew(0);
// work with it
ksDel (keys);


 goes ok, the alloc size will be 16, defined in kdbprivate.h. The alloc size will be doubled whenever size reaches alloc size, so it also performs out large keysets.

But if you have any clue how large your keyset may be you should read the next statements.

If you want a keyset with length 15 (because you know of your application that you normally need about 12 up to 14 keys), use:

KeySet * keys = ksNew (15, KS_END);
// work with it
ksDel (keys);

If you start having 3 keys, and your application needs approximately 200-500 keys, you can use:

KeySet * config = ksNew (500,
        keyNew ('user/sw/app/fixedConfiguration/key1', KEY_SWITCH_VALUE, 'value1', 0),
        keyNew ('user/sw/app/fixedConfiguration/key2', KEY_SWITCH_VALUE, 'value2', 0),
        keyNew ('user/sw/app/fixedConfiguration/key3', KEY_SWITCH_VALUE, 'value3', 0),
        KS_END); // don't forget the KS_END at the end!
// work with it
ksDel (config);


 Alloc size is 500, the size of the keyset will be 3 after ksNew. This means the keyset will reallocate when appending more than 497 keys.

The main benefit of taking a list of variant length parameters is to be able to have one C-Statement for any possible KeySet.

Due to ABI compatibility, the KeySet structure is only declared in kdb.h, and not defined. So you can only declare pointers to KeySets in your program. See http://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html#AEN135

See also:

ksDel() to free the KeySet :: Class Methods afterwards

ksDup() to duplicate an existing KeySet :: Class Methods

Parameters:

alloc gives a hint for the size how many Keys may be stored initially

Returns:

a ready to use KeySet object

0 on memory error

 

Key* ksNext (KeySet * ks)Returns the next Key in a KeySet.

KeySets have an internal cursor that can be reset with ksRewind(). Every time ksNext() is called the cursor is incremented and the new current Key is returned.

You'll get a NULL pointer if the key after the end of the KeySet was reached. It will set the cursor to the beginning of the KeySet and the next time the first key is returned.

The ks internal cursor will be changed, so it is not const.

Note:

You must not delete or change the key, use ksPop() if you want to delete it.

Parameters:

ks the keyset object to work with

Returns:

the new current Key

0 when the end is reached

0 on NULL pointer

See also:

ksRewind(), ksCurrent()

 

Key* ksPop (KeySet * ks)Remove and return the last key of ks.

The reference counter will be decremented by one.

The KeySets cursor will not be effected if it did not point to the popped key.

Note:

You need to keyDel() the key afterwards, if you don't append it to another keyset. It has the same semantics like a key allocated with keyNew() or keyDup().

ks1=ksNew(0);
ks2=ksNew(0);

k1=keyNew(0); // ref counter 0
ksAppendKey(ks1, k1); // ref counter 1
ksAppendKey(ks2, k1); // ref counter 2

k1=ksPop (ks1); // ref counter 1
k1=ksPop (ks2); // ref counter 0, like after keyNew()

ksAppendKey(ks1, k1); // ref counter 1

ksDel (ks1); // key is deleted too
ksDel (ks2);
 *

Returns:

the last key of ks

NULL if ks is empty or on NULL pointer

Parameters:

ks KeySet to work with

See also:

ksAppendKey(), ksAppend()

commandList() for an example

 

int ksRewind (KeySet * ks)Rewinds the KeySet internal cursor.

Use it to set the cursor to the beginning of the KeySet. ksCurrent() will then always return NULL afterwards. So you want to ksNext() first.

ksRewind (ks);
while ((key = keyNext (ks))!=0) {}

Parameters:

ks the keyset object to work with

Returns:

0 on success

-1 on NULL pointer

See also:

ksNext(), ksCurrent()

 

int ksSetCursor (KeySet * ks, cursor_t cursor)Set the KeySet internal cursor.

Use it to set the cursor to a stored position. ksCurrent() will then be the position which you got with.

Warning:

Cursors may get invalid when the key was ksPop()ed or ksLookup() was used together with KDB_O_POP.

cursor_t cursor;
// key now in any position here
cursor = ksGetCursor (ks);
while ((key = keyNext (ks))!=0) {}
ksSetCursor (ks, cursor); // reset state
ksCurrent(ks); // in same position as before

An invalid cursor will set the keyset to its beginning like ksRewind(). When you set an invalid cursor ksCurrent() is 0 and ksNext() == ksHead().

Parameters:

cursor the cursor to use
ks the keyset object to work with

Returns:

0 when the keyset is ksRewind()ed

1 otherwise

-1 on NULL pointer

See also:

ksNext(), ksGetCursor()

 

void ksSort (KeySet * ks)Sorts a KeySet alphabetically by Key name.

You need ksSort() only in few cases directly.  

Don't need to sort before using ksLookup

You don't need it if you just just kdbGet() and subsequent ksLookup().

KeySet *ks = ksNew(0);
kdbGet(h, ks, k, 0);
// ksPop(), ksAppend() and ksAppendKey() allowed here
ksLookup(ks, s, 0); // you don't need to sort ks

This is because the KeySet tracks if it needs to be sorted and ksLookup() will sort when needed.  

Sort when iterating

Before you iterate over a keyset you have to sort it, if you need it in a sorted way.

To achieve that you can pass option_t::KDB_O_SORT to kdbGet() and kdbSet(). Then you will receive a already sorted keyset over which you can iterate.

KeySet *ks = ksNew(0);
kdbGet(h, ks, k, KDB_O_SORT);
// no changes to keyset allowed
ksRewind(ks);
// now you can iterate over a sorted keyset

Its of course also possible to use ksLookup() once, because it will sort the keyset too.  

Sort when changing key

Warning:

You should not use keySetName() or keyRemove() when a key belongs to a keyset. When you are doing this, you always need to manually sort all keysets where the key was before using ksLookup() (otherwise ksLookup() won't find that keys), kdbGet() or kdbSet() methods.

When you change a key's name or its remove status the order which was previously correctly is then wrong. The keyset does not recognize this, so the programmer has to take care that ksSort() is called before any operation which needs a sorted keyset (which are all ksLookup(), all kdbGet() and all kdbSet() functions).

Note:

You can remember that easily that all functions which get options require one of the following:
that you did not manipulate a keys name or a remove status
that you pass KDB_O_SORT when you know that you manipulated at least one key
that you ksSort() yourself after manipulating keys

 

Dirty KeySet

When you use ksAppend(), ksAppendKey(), ksPop() the keyset is dirty afterwards, which means that it needs to be sorted. This is done automatically using a ksLookup() method and in ksGet() or ksSet() (All methods which accept options).

It won't be done if you just iterate over the keyset, so you might use a ksLookup() or ksSort() first. ksLookup() will be more efficient in that case, because it will only sort when needed. Don't pass KDB_O_NOALL (it will deactivate the sorting feature), see ksLookup() for more information.

Parameters:

ks KeySet to be sorted

See also:

kdbGet(), kdbSet(), ksLookup() for some functions which may need sorting before they are called. (All functions which take options as arguments)

keySetName(), keySetBaseName(), keyAddBaseName() and keyRemove() for all methods which change the sorting state where the KeySet :: Class Methods can't track the change.

ksAppend(), ksAppendKey(), ksPop() for all methods which make a KeySet :: Class Methods dirty.

 

Key* ksTail (const KeySet * ks)Return the last key in the KeySet.

The KeySets cursor will not be effected.

If ksCurrent()==ksTail() you know you are on the last key. ksNext() will return a NULL pointer afterwards.

Parameters:

ks the keyset object to work with

Returns:

the last Key of a keyset

0 on NULL pointer or empty keyset

See also:

ksHead() for the first Key :: Basic Methods

ksRewind(), ksCurrent() and ksNext() for iterating over the KeySet :: Class Methods

 

Author

Generated automatically by Doxygen for Elektra Projekt from the source code.


 

Index

NAME
Functions
Detailed Description
Function Documentation
ssize_t ksAppend (KeySet * ks, const KeySet * toAppend)Append all toAppend contained keys to the end of the ks.
ssize_t ksAppendKey (KeySet * ks, Key * toAppend)Appends a Key to the end of ks.
int ksCopy (KeySet * dest, const KeySet * source)Copy a keyset.
Key* ksCurrent (const KeySet * ks)Return the current Key.
int ksDel (KeySet * ks)A destructor for KeySet objects.
KeySet* ksDup (const KeySet * source)Return a duplicate of a keyset.
cursor_t ksGetCursor (const KeySet * ks)Get the KeySet internal cursor.
Read ahead
Restoring state
ssize_t ksGetSize (const KeySet * ks)Return the number of keys that ks contains.
Key* ksHead (const KeySet * ks)Return the first key in the KeySet.
Key* ksLookup (KeySet * ks, Key * key, option_t options)Look for a Key contained in ks that matches the name of the key.
Introduction
Usage
KDB_O_NOALL
KDB_O_POP
Key* ksLookupByName (KeySet * ks, const char * name, option_t options)Look for a Key contained in ks that matches name.
Cascading
Full Search
KeySet* ksNew (size_t alloc, ...)Allocate, initialize and return a new KeySet object.
Key* ksNext (KeySet * ks)Returns the next Key in a KeySet.
Key* ksPop (KeySet * ks)Remove and return the last key of ks.
int ksRewind (KeySet * ks)Rewinds the KeySet internal cursor.
int ksSetCursor (KeySet * ks, cursor_t cursor)Set the KeySet internal cursor.
void ksSort (KeySet * ks)Sorts a KeySet alphabetically by Key name.
Don't need to sort before using ksLookup
Sort when iterating
Sort when changing key
Dirty KeySet
Key* ksTail (const KeySet * ks)Return the last key in the KeySet.
Author

This document was created by man2html, using the manual pages.
Time: 21:48:55 GMT, April 16, 2011