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Elektra 0.11.0
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A keyset holds together a set of keys. More...
#include <keyset.hpp>
Public Member Functions | |
KeySet () | |
Creates a new empty keyset with no keys. More... | |
KeySet (ckdb::KeySet *k) | |
Take ownership of a ckdb::KeySet * . More... | |
KeySet (const KeySet &other) | |
Duplicate a keyset. More... | |
KeySet (size_t alloc,...) ELEKTRA_SENTINEL | |
Create a new keyset. More... | |
KeySet (VaAlloc alloc, va_list ap) | |
Create a new keyset. More... | |
~KeySet () | |
Deconstruct a keyset. More... | |
ckdb::KeySet * | release () |
If you don't want destruction of keyset at the end you can release the pointer. | |
ckdb::KeySet * | getKeySet () const |
Passes out the raw keyset pointer. More... | |
KeySet & | operator= (KeySet const &other) |
Duplicate a keyset. More... | |
ssize_t | size () const |
The size of the keyset. More... | |
KeySet | dup () const |
Duplicate a keyset. More... | |
void | copy (const KeySet &other) |
Copy a keyset. More... | |
void | clear () |
Clear the keyset. More... | |
ssize_t | append (const Key &toAppend) |
append a key More... | |
ssize_t | append (const KeySet &toAppend) |
append a keyset More... | |
Key | pop () |
Remove and return the last Key of ks . More... | |
Key | at (elektraCursor pos) const |
Lookup a key by index. More... | |
KeySet | cut (const Key &k) |
Cuts out all Keys from KeySet ks that are below or at cutpoint . More... | |
KeySet | cut (std::string const &name) |
Cuts out all Keys from KeySet ks that are below or at cutpoint . More... | |
Key | lookup (const Key &k, const elektraLookupFlags options=KDB_O_NONE) const |
Look for a Key contained in ks that matches the name of the key . More... | |
Key | lookup (std::string const &name, const elektraLookupFlags options=KDB_O_NONE) const |
Lookup a key by name. More... | |
template<typename T > | |
T | get (std::string const &name, const elektraLookupFlags options=KDB_O_NONE) const |
Generic lookup+get for keysets. More... | |
ssize_t | search (const Key &toSearch) const |
Search in a key set, either yielding the actual index of the key, if the key has been found within the key set, or a negative value indicating the insertion index of the key, if the key would be inserted. More... | |
ssize_t | search (std::string const &name) const |
Search in a key set, either yielding the actual index of the key, if the key has been found within the key set, or a negative value indicating the insertion index of the key, if the key would be inserted. More... | |
A keyset holds together a set of keys.
Methods to manipulate KeySets. A KeySet is a set of keys.
Most important properties of a KeySet:
The most important methods of KeySet:
KeySet is the most important data structure in 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 and it can be used in plugins to manipulate or check configuration.
With ksLookupByName() it is possible to fetch easily specific keys out of the list of keys.
You can easily create and iterate keys:
Keysets employ copy-on-write techniques to minimize memory footprint. If you create a copy or a duplication of a keyset, the resulting keyset initially references the same data as the source keyset. Only if add or remove keys from a keyset additional memory is allocated.
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Creates a new empty keyset with no keys.
Allocate, initialize and return a new KeySet object. Objects created with ksNew() must be destroyed with ksDel().
You can use an arbitrary 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 KS_END.
So, terminate with ksNew(0, KS_END) or ksNew(20, ..., KS_END)
The first parameter alloc
defines how many Keys can be added without reallocation. If you pass any alloc size greater than 0, but less than 16, it will default to 16.
For most uses
will be fine. The alloc size will be 16 and will double whenever size reaches alloc size, so it also performs well with large KeySets.
You can defer the allocation of the internal array that holds the Keys, by passing 0 as the alloc size. This is useful if it is unclear whether your KeySet will actually hold any Keys and you want to avoid a malloc call.
If the size of the KeySet is known in advance, use the alloc
parameter to hint the size of the KeySet.
If your application only needs up to 15 Keys you can request a KeySet of size 15:
If you start having 3 Keys, and your application needs approximately 200 up to 500 Keys, you can use:
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. If you prefer, you can always create an empty KeySet and use ksAppendKey().
alloc | gives a hint for how many Keys may be stored initially |
0 | on memory error |
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Duplicate a keyset.
This keyset will be a duplicate of the other afterwards.
So it is shallow copy, to create a deep copy you have to dup() every key (it still won't copy metadata, but they are COW):
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Create a new keyset.
alloc | minimum number of keys to allocate |
... | variable argument list |
Allocate, initialize and return a new KeySet object. Objects created with ksNew() must be destroyed with ksDel().
You can use an arbitrary 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 KS_END.
So, terminate with ksNew(0, KS_END) or ksNew(20, ..., KS_END)
The first parameter alloc
defines how many Keys can be added without reallocation. If you pass any alloc size greater than 0, but less than 16, it will default to 16.
For most uses
will be fine. The alloc size will be 16 and will double whenever size reaches alloc size, so it also performs well with large KeySets.
You can defer the allocation of the internal array that holds the Keys, by passing 0 as the alloc size. This is useful if it is unclear whether your KeySet will actually hold any Keys and you want to avoid a malloc call.
If the size of the KeySet is known in advance, use the alloc
parameter to hint the size of the KeySet.
If your application only needs up to 15 Keys you can request a KeySet of size 15:
If you start having 3 Keys, and your application needs approximately 200 up to 500 Keys, you can use:
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. If you prefer, you can always create an empty KeySet and use ksAppendKey().
alloc | gives a hint for how many Keys may be stored initially |
0 | on memory error |
alloc | the allocation size |
va | the list of variable arguments |
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Create a new keyset.
alloc | minimum number of keys to allocate |
ap | variable arguments list |
Use va as first argument to use this constructor, e.g.:
Allocate, initialize and return a new KeySet object. Objects created with ksNew() must be destroyed with ksDel().
You can use an arbitrary 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 KS_END.
So, terminate with ksNew(0, KS_END) or ksNew(20, ..., KS_END)
The first parameter alloc
defines how many Keys can be added without reallocation. If you pass any alloc size greater than 0, but less than 16, it will default to 16.
For most uses
will be fine. The alloc size will be 16 and will double whenever size reaches alloc size, so it also performs well with large KeySets.
You can defer the allocation of the internal array that holds the Keys, by passing 0 as the alloc size. This is useful if it is unclear whether your KeySet will actually hold any Keys and you want to avoid a malloc call.
If the size of the KeySet is known in advance, use the alloc
parameter to hint the size of the KeySet.
If your application only needs up to 15 Keys you can request a KeySet of size 15:
If you start having 3 Keys, and your application needs approximately 200 up to 500 Keys, you can use:
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. If you prefer, you can always create an empty KeySet and use ksAppendKey().
alloc | gives a hint for how many Keys may be stored initially |
0 | on memory error |
alloc | the allocation size |
va | the list of variable arguments |
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Deconstruct a keyset.
A destructor for KeySet objects. Every KeySet created by ksNew() must be deleted with ksDel().
When the reference counter of ks
is non-zero, this function will do nothing and simply return the current value of the reference counter.
It is therefore safe to call ksDel (ks)
on any KeySet * ks
.
ks | the KeySet object to delete |
0 | when the KeySet was freed |
-1 | on NULL pointers |
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append a key
toAppend | key to append |
Appends a Key to the end of ks
. Hands the ownership of the Key toAppend
to the KeySet ks
. ksDel(ks) uses keyDel(k) to delete every Key unless it got its reference counter incremented by keyIncRef(), e.g. by another KeySet that contains this Key.
The reference counter of the Key will be incremented to indicate this ownership, and thus toAppend
is not const.
If the Key's name already exists in the KeySet, it will be replaced with the new Key.
ksAppendKey() will also lock the Key's name from toAppend
. This is necessary so that the order of the KeySet cannot be destroyed via calls to keySetName().
The KeySet internal cursor will be set to the new Key.
It is safe to directly append newly created Keys:
If you want the key to outlive the KeySet, make sure to do proper ref counting:
You can duplicate the Key to avoid aliasing, but then the Key in the KeySet has another identity:
ks | KeySet where toAppend should be append |
toAppend | Key that will be appended to ks or deleted |
-1 | on NULL pointers |
-1 | if appending failed (only on memory problems). The Key will be deleted then. |
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append a keyset
toAppend | keyset to append |
Append all Keys in toAppend
to the end of the KeySet ks
. toAppend
KeySet will be left unchanged.
If a Key is both in toAppend
and ks
, the Key in ks
will be overwritten.
ks | the KeySet that will receive the Keys |
toAppend | the KeySet that provides the Keys that will be transferred |
ks
after transfer -1 | on NULL pointers |
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Lookup a key by index.
pos | cursor position |
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Clear the keyset.
Keyset will be empty afterwards.
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Copy a keyset.
Replaces all keys in this
with the ones from other
. This is only a shallow copy. For a deep copy you need to manually Key::dup every key.
other | other keyset to copy |
Replace the content of a KeySet with another one. Most often you may want a duplicate of a KeySet, see ksDup() or append keys, see ksAppend(). In some situations you need to copy Keys from a KeySet to another KeySet, for which this function exists.
source
.dest
will be deleted. Afterwards the content of source
will be added to the destination.A flat copy is made, so Keys will not be duplicated, but their reference counter is updated, so both KeySets need to be deleted via ksDel().
source | an initialized KeySet or NULL |
dest | an initialized KeySet, where the Keys from source get copied to |
1 | on success |
0 | if dest was cleared successfully (source is NULL) |
-1 | when dest is a NULL pointer |
Cuts out all Keys from KeySet ks
that are below or at cutpoint
.
Searches for the cutpoint
inside the KeySet ks
. If found, it cuts out this Key and everything which is below (see keyIsBelow()) this Key. These Keys will be missing in the keyset ks
. Instead, they will be moved to the returned KeySet. If cutpoint
is not found an empty KeySet is returned and ks
is not changed.
The cursor will stay at the same Key as it was before. If the cursor was inside the region of cut (moved) Keys, the cursor will be set to the Key before the cutpoint
.
If you use ksCut() on a KeySet you got from kdbGet() and plan to use kdbSet() later, make sure that you keep all Keys that should not be removed permanently. You have to keep the KeySet that was returned and the KeySet ks
.
You have the keyset ks:
system:/mountpoint/interest
system:/mountpoint/interest/folder
system:/mountpoint/interest/folder/key1
system:/mountpoint/interest/folder/key2
system:/mountpoint/other/key1
When you use
Then in returned
are:
system:/mountpoint/interest
system:/mountpoint/interest/folder
system:/mountpoint/interest/folder/key1
system:/mountpoint/interest/folder/key2
And in ks
are:
system:/mountpoint/other/key1
So kdbSet() permanently removes all keys at or below system:/mountpoint/interest
.
ks | the Keyset to cut. It will be modified by removing all Keys at or below the cutpoint. |
cutpoint | the point where to cut out the Keyset |
0 | on NULL pointers, no Key name or allocation problems |
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Cuts out all Keys from KeySet ks
that are below or at cutpoint
.
Searches for the cutpoint
inside the KeySet ks
. If found, it cuts out this Key and everything which is below (see keyIsBelow()) this Key. These Keys will be missing in the keyset ks
. Instead, they will be moved to the returned KeySet. If cutpoint
is not found an empty KeySet is returned and ks
is not changed.
The cursor will stay at the same Key as it was before. If the cursor was inside the region of cut (moved) Keys, the cursor will be set to the Key before the cutpoint
.
If you use ksCut() on a KeySet you got from kdbGet() and plan to use kdbSet() later, make sure that you keep all Keys that should not be removed permanently. You have to keep the KeySet that was returned and the KeySet ks
.
You have the keyset ks:
system:/mountpoint/interest
system:/mountpoint/interest/folder
system:/mountpoint/interest/folder/key1
system:/mountpoint/interest/folder/key2
system:/mountpoint/other/key1
When you use
Then in returned
are:
system:/mountpoint/interest
system:/mountpoint/interest/folder
system:/mountpoint/interest/folder/key1
system:/mountpoint/interest/folder/key2
And in ks
are:
system:/mountpoint/other/key1
So kdbSet() permanently removes all keys at or below system:/mountpoint/interest
.
ks | the Keyset to cut. It will be modified by removing all Keys at or below the cutpoint. |
cutpoint | the point where to cut out the Keyset |
0 | on NULL pointers, no Key name or allocation problems |
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Duplicate a keyset.
This is only a shallow copy. For a deep copy you need to dup every key.
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 their reference counter is updated, so both KeySets need to be deleted via ksDel().
source | has to be an initialized KeySet |
0 | on NULL pointer |
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Generic lookup+get for keysets.
name | the key name to get |
options | the options to be passed to lookup() |
KeyNotFoundException | if no key found |
Use
to include specializations for std types.
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Passes out the raw keyset pointer.
This function exists so that pure C functions that do not have a C++ binding can be called.
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Look for a Key contained in ks
that matches the name of the key
.
/
). Furthermore, a lookup should be done for every Key (also when iterating over Keys) so that the specifications are honored correctly. Keys of all namespaces need to be present so that ksLookup() can work correctly, so make sure to also use kdbGet() with a cascading Key.ksLookup() is designed to let you work with a KeySet containing all Keys of the application. The idea is to fully kdbGet() the whole configuration of your application and process it all at once with many ksLookup()
.
This function is efficient (at least using binary search). Together with kdbGet(), which you can use to load the whole configuration, you can write very effective and short code for configuration:
This is the way programs should get their configuration and search for the values. It is guaranteed, that more namespaces can be added easily and that all values can be set by admin and user. Furthermore, using the kdb-tool, it is possible to introspect which values an application will get (by doing the same cascading lookup).
If found, a pointer to the Key is returned. If not found a NULL pointer is returned.
Cascading lookups will by default search in all namespaces (proc:/, dir:/, user:/ and system:/), but will also correctly consider the specification (=metadata) in spec:/:
override/#
will make sure that another Key is considered beforenamespace/#
will change the number and/or order in which the namespaces are searchedfallback/#
will search for other Keys when the other possibilities up to now were not successfuldefault
to return the given value when not even fallback
Keys were found.This process is very flexible, but it would be boring to manually follow all this links to find out which Key will be taken in the end. Use kdb get -v
to trace the Keys.
This is also a nice example how a complete application with ksLookup() can look like.
ENABLE_OPTIMIZATIONS=ON
a hybrid search decides dynamically between the binary search and the OPMPHM. The hybrid search can be overruled by passing KDB_O_OPMPHM or KDB_O_BINSEARCH in the options to ksLookup().ks | the KeySet that should be searched |
key | the Key object you are looking for |
options | of type elektraLookupFlags with some KDB_O_* option bits - as explained above |
0 | if no Key has been found |
0 | on NULL pointers |
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Lookup a key by name.
name | the name to look for |
options | some options to pass |
Duplicate a keyset.
This keyset will be a duplicate of the other afterwards.
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Remove and return the last Key of ks
.
The reference counter of the Key will be decremented by one.
The KeySet's cursor will not be affected if it did not point to the popped Key.
ks
NULL | if ks is empty or a NULL pointer |
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Search in a key set, either yielding the actual index of the key, if the key has been found within the key set, or a negative value indicating the insertion index of the key, if the key would be inserted.
ks | the keyset to work with |
key | the key to check |
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Search in a key set, either yielding the actual index of the key, if the key has been found within the key set, or a negative value indicating the insertion index of the key, if the key would be inserted.
ks | the keyset to work with |
key | the key to check |
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The size of the keyset.