Elektra  0.8.23
Modules | Enumerations | Functions
Key

Key is an essential class that encapsulates key name , value and metainfo . More...

Collaboration diagram for Key:

Modules

 Meta Info Manipulation Methods
 Methods to do various operations on Key metadata.
 
 Methods for Making Tests
 Methods to do various tests on Keys.
 
 Name Manipulation Methods
 Methods to do various operations on Key names.
 
 Value Manipulation Methods
 Methods to do various operations on Key values.
 

Enumerations

enum  keyswitch_t {
  KEY_NAME =1, KEY_VALUE =1<<1, KEY_FLAGS =3, KEY_OWNER =1<<2,
  KEY_COMMENT =1<<3, KEY_BINARY =1<<4, KEY_UID =1<<5, KEY_GID =1<<6,
  KEY_MODE =1<<7, KEY_ATIME =1<<8, KEY_MTIME =1<<9, KEY_CTIME =1<<10,
  KEY_SIZE =1<<11, KEY_DIR =1<<14, KEY_META =1<<15, KEY_NULL =1<<16,
  KEY_CASCADING_NAME =1<<20, KEY_META_NAME =1<<21, KEY_END =0
}
 Allows keyNew() to determine which information comes next. More...
 
enum  elektraNamespace {
  KEY_NS_NONE =0, KEY_NS_EMPTY =1, KEY_NS_META =2, KEY_NS_CASCADING =3,
  KEY_NS_FIRST =4, KEY_NS_SPEC =4, KEY_NS_PROC =5, KEY_NS_DIR =6,
  KEY_NS_USER =7, KEY_NS_SYSTEM =8, KEY_NS_LAST =8
}
 Elektra currently supported Key namespaces. More...
 

Functions

Key * keyNew (const char *name,...)
 A practical way to fully create a Key object in one step. More...
 
Key * keyDup (const Key *source)
 Return a duplicate of a key. More...
 
int keyCopy (Key *dest, const Key *source)
 Copy or Clear a key. More...
 
int keyDel (Key *key)
 A destructor for Key objects. More...
 
int keyClear (Key *key)
 Key Object Cleaner. More...
 
ssize_t keyIncRef (Key *key)
 Increment the viability of a key object. More...
 
ssize_t keyDecRef (Key *key)
 Decrement the viability of a key object. More...
 
ssize_t keyGetRef (const Key *key)
 Return how many references the key has. More...
 

Detailed Description

Key is an essential class that encapsulates key name , value and metainfo .

To use it include:

#include <kdb.h>

Key properties are:

ABI
Due to ABI compatibility, the Key structure is not defined in kdb.h, only declared. So you can only declare pointers to Keys in your program, and allocate and free memory for them with keyNew() and keyDel() respectively.
Reference Counting
Every key has its reference counter (see keyGetRef() for longer explanation) that will be initialized with 0, that means a subsequent call of keyDel() will delete the key. If you append the key to a keyset the reference counter will be incremented by one (see keyIncRef()) and the key can't be deleted by a keyDel().
As you can imagine this refcounting allows you to put the Key in your own data structures. It can be a very powerful feature, e.g. if you need your own-defined ordering or different Models of your configuration.

Enumeration Type Documentation

Elektra currently supported Key namespaces.

See also
kdbGet(), keyGetNamespace()
Enumerator
KEY_NS_NONE 

no key given as parameter to keyGetNamespace()

KEY_NS_EMPTY 

key name was empty, e.g. invalid key name

KEY_NS_META 

metakey, i.e. any key name not under other categories

KEY_NS_CASCADING 

cascading key, starts with /, abstract name for any of the namespaces below

KEY_NS_FIRST 

For iteration over namespaces (first element, inclusive)

KEY_NS_SPEC 

spec contains the specification of the other namespaces

KEY_NS_PROC 

proc contains process-specific configuration

KEY_NS_DIR 

dir contains configuration from a specific directory

KEY_NS_USER 

user key in the home directory of the current user

KEY_NS_SYSTEM 

system key is shared for a computer system

KEY_NS_LAST 

For iteration over namespaces (last element, inclusive)

Allows keyNew() to determine which information comes next.

See also
keyNew()
Enumerator
KEY_NAME 

Flag for the key name

KEY_VALUE 

Flag for the key data

KEY_FLAGS 

Allows to define multiple flags at once.

KEY_OWNER 

Flag for the key user domain

KEY_COMMENT 

Flag for the key comment

KEY_BINARY 

Flag if the key is binary

KEY_UID 

Flag for the key UID

Deprecated:
do not use
KEY_GID 

Flag for the key GID

Deprecated:
do not use
KEY_MODE 

Flag for the key permissions

Deprecated:
do not use
KEY_ATIME 

Flag for the key access time

Deprecated:
do not use
KEY_MTIME 

Flag for the key change time

Deprecated:
do not use
KEY_CTIME 

Flag for the key status change time

Deprecated:
do not use
KEY_SIZE 

Flag for maximum size to limit value

KEY_DIR 

Flag for the key directories

Deprecated:
do not use
KEY_META 

Flag for metadata

KEY_NULL 

Is not a flag, only as return value

Deprecated:
do not use
KEY_CASCADING_NAME 

Is default, no need to use it

Deprecated:
do not use
KEY_META_NAME 

Allow any key names (not only with known namespaces+cascading

KEY_END 

Used as a parameter terminator to keyNew()

Function Documentation

int keyClear ( Key *  key)

Key Object Cleaner.

Will reset all internal data.

After this call you will receive a fresh key.

The reference counter will stay unmodified.

Note
that you might also clear() all aliases with this operation.
1 int f (Key *k)
2 {
3  keyClear (k);
4  // you have a fresh key k here
5  keySetString (k, "value");
6  // the caller will get an empty key k with an value
7 }
Return values
returns0 on success
-1on null pointer
Parameters
keythe key object to work with
int keyCopy ( Key *  dest,
const Key *  source 
)

Copy or Clear a key.

Most often you may prefer keyDup() which allocates a new key and returns a duplication of another key.

But when you need to copy into an existing key, e.g. because it was passed by a pointer in a function you can do so:

void h (Key * k)
{
// receive key c
keyCopy (k, c);
// the caller will see the changed key k
}

The reference counter will not be changed for both keys. Affiliation to keysets are also not affected.

The metadata will be duplicated for the destination key. So it will not take much additional space, even with lots of metadata.

When you pass a NULL-pointer as source the data of dest will be cleaned completely (except reference counter, see keyClear()) and you get a fresh dest key:

void g (Key * k)
{
keyCopy (k, 0);
// k is now an empty and fresh key
}

If you want to copy everything, except e.g. the value you can use keyCopy() too:

void j (Key * k)
{
size_t size = keyGetValueSize (k);
char * value = malloc (size);
int bstring = keyIsString (k);
// receive key c
memcpy (value, keyValue (k), size);
keyCopy (k, c);
if (bstring)
keySetString (k, value);
else
keySetBinary (k, value, size);
free (value);
// the caller will see the changed key k
// with the name and metadata from c (except
// metadata "binary", which stayed the same)
}

Restrain from coping everything yourself, because it will lead to wrong metadata and is not able to copy empty or cascading names:

void i (Key * k)
{
keySetName (k, keyName (c));
// k is not a copy of c even if everything was successfully,
// because it still contains metadata from k
}
Parameters
destthe key which will be written to
sourcethe key which should be copied or NULL to clean the destination key
Return values
-1on failure when a NULL pointer was passed for dest or a dynamic property could not be written. The content will be unmodified then.
0when dest was cleaned
1when source was successfully copied
See also
keyDup() to get a duplication of a Key
ssize_t keyDecRef ( Key *  key)

Decrement the viability of a key object.

The references will be decremented for ksPop() or successful calls of ksLookup() with the option KDB_O_POP. It will also be decremented with an following keyDel() in the case that an old key is replaced with another key with the same name.

The reference counter can't be decremented once it reached 0. In that situation nothing will happen and 0 will be returned.

Note
keyDup() will reset the references for dupped key.
Returns
the value of the new reference counter
Return values
-1on null pointer
0when the key is ready to be freed
Parameters
keythe key object to work with
See also
keyGetRef() for longer explanation, keyDel(), keyIncRef()
int keyDel ( Key *  key)

A destructor for Key objects.

Every key created by keyNew() must be deleted with keyDel().

It is save to delete keys which are in a keyset, the number of references will be returned then.

It is save to delete a nullpointer, -1 will be returned then.

It is also save to delete a multiple referenced key, nothing will happen then and the reference counter will be returned.

Parameters
keythe key object to delete
See also
keyNew(), keyIncRef(), keyGetRef()
Returns
the value of the reference counter if the key is within keyset(s)
Return values
0when the key was freed
-1on null pointers
Key* keyDup ( const Key *  source)

Return a duplicate of a key.

Memory will be allocated as needed for dynamic properties.

The new key will not be member of any KeySet and will start with a new reference counter at 0. A subsequent keyDel() will delete the key.

1 int f (const Key * source)
2 {
3  Key * dup = keyDup (source);
4  // work with duplicate
5  keyDel (dup);
6  // everything related to dup is freed
7  // and source is unchanged
8 }

Like for a new key after keyNew() a subsequent ksAppend() makes a KeySet to take care of the lifecycle of the key.

1 int g (const Key * source, KeySet * ks)
2 {
3  Key * dup = keyDup (source);
4  // work with duplicate
5  ksAppendKey (ks, dup);
6  // ksDel(ks) will also free the duplicate
7  // source remains unchanged.
8 }

Duplication of keys should be preferred to keyNew(), because data like owner can be filled with a copy of the key instead of asking the environment. It can also be optimized in the checks, because the keyname is known to be valid.

Parameters
sourcehas to be an initialized source Key
Return values
0failure or on NULL pointer
Returns
a fully copy of source on success
See also
ksAppend(), keyDel(), keyNew()
ssize_t keyGetRef ( const Key *  key)

Return how many references the key has.

The reference counting is the essential property of keys to make sure that they can be put safely into data structures. E.g. if you put a Key into a KeySet:

Key *k = keyNew("user/proper_name", KEY_END); // ref counter = 0
KeySet *ks = ksNew (1, k, KS_END);
keyDel(k); // key will not be deleted, because its in the keyset
ksDel(ks); // now the key will be deleted

You can even add the key to more KeySets:

Key *k = keyNew("user/proper_name", KEY_END); // ref counter 0
KeySet *ks1 = ksNew(1, k, KS_END); // ref counter of k 1
KeySet *ks2 = ksNew(1, k, KS_END); // ref counter of k 2
ksDel(ks1); // ref counter of k 1
ksDel(ks2); // k is now deleted

If you increment only by one with keyIncRef() the same as said above is valid:

Key *k = keyNew(0); // ref counter = 0
keyIncRef(k); // ref counter = 1
keyDel(k); // key will not be deleted
keyDel(k);

or use keyIncRef() more than once:

Key *k = keyNew(0); // ref counter 0
keyIncRef(k); // ref counter of key 1
keyDel (k); // has no effect
keyIncRef(k); // ref counter of key 2
keyDel (k); // has no effect
keyDecRef(k); // ref counter of key 1
keyDel (k); // has no effect
keyDecRef(k); // ref counter is now 0
keyDel (k); // k is now deleted

The key won't be deleted by a keyDel() as long refcounter is not 0.

The references will be incremented on successful calls to ksAppendKey() or ksAppend().

Note
keyDup() will reset the references for dupped key.

For your own applications you can use keyIncRef() and keyDecRef() for reference counting, too.

Parameters
keythe key object to work with
Returns
the number of references
Return values
-1on null pointer
See also
keyIncRef() and keyDecRef()
ssize_t keyIncRef ( Key *  key)

Increment the viability of a key object.

This function is intended for applications using their own reference counter for key objects. With it you can increment the reference and thus avoid destruction of the object in a subsequent keyDel().

The reference counter can't be incremented once it reached SSIZE_MAX. In that situation nothing will happen and SSIZE_MAX will be returned.

Note
keyDup() will reset the references for dupped key.
Returns
the value of the new reference counter
Return values
-1on null pointer
SSIZE_MAXwhen maximum exceeded
Parameters
keythe key object to work with
See also
keyGetRef() for longer explanation, keyDecRef(), keyDel()
Key* keyNew ( const char *  name,
  ... 
)

A practical way to fully create a Key object in one step.

To just get a key object, simple do:

Key *k = keyNew(0);
// work with it
keyDel (k);

If you want the key object to contain a name, value, comment and other meta info read on.

Note
When you already have a key with similar properties its easier to keyDup() the key.

You can call it in many different ways depending on the attribute tags you pass as parameters. Tags are represented as keyswitch_t values, and tell keyNew() which Key attribute comes next.

We can also give an empty key name and a KEY_END tag with the same effect as before:

Key *k =keyNew("", KEY_END); // Has the same effect as above
// work with it
keyDel (k);

But we can also give the key a proper name right from the start:

// Create and initialize a key with a name and nothing else
Key *k=keyNew("user/some/example", KEY_END);
// work with it
keyDel (k);

So, keyNew() allocates memory for a key object and keyDel() cleans everything up.

keyNew() processes the given argument list even further. The Key attribute tags are the following:

  • KEY_VALUE
    Next parameter is a pointer to the value that will be used. If no KEY_BINARY was used before, a string is assumed.
    // Create and initialize a key with a name and nothing else
    Key *k=keyNew("user/tmp/ex0",
    KEY_VALUE, "some data", // set a string value
    KEY_END); // end of args
  • KEY_SIZE
    Define a maximum length of the value. This is only used when setting a binary key.
    // Create and initialize a key with a name and nothing else
    Key *k=keyNew("user/tmp/ex1",
    KEY_SIZE, 4, // has no effect on strings
    KEY_VALUE, "some data", // set a string value
    KEY_END); // end of args
  • KEY_META
    Next two parameter is a metaname and a metavalue. See keySetMeta().
    Key *k=keyNew("user/tmp/ex3",
    KEY_META, "comment", "a comment", // with a comment
    KEY_META, "owner", "root", // and an owner
    KEY_META, "special", "yes", // and any other metadata
    KEY_END); // end of args
  • KEY_END
    Must be the last parameter passed to keyNew(). It is always required, unless the keyName is 0.
  • KEY_FLAGS
    Bitwise disjunction of flags, which don't require one or more values. recommended way to set multiple flags. overrides previously defined flags.
    Key *k=keyNew("user/tmp/ex3",
    KEY_SIZE, 7, // assume binary length 7
    KEY_VALUE, "some data", // value that will be truncated in 7 bytes
    KEY_END); // end of args
  • KEY_BINARY
    Allows one to change the key to a binary key. Make sure that you also pass KEY_SIZE before you set the value. Otherwise it will be cut off with first \0 in the string. So this flag toggle from keySetString() to keySetBinary(). If no value (nor size) is given, it will be a NULL key.
    // Create and initialize a key with a name and nothing else
    Key *k=keyNew("user/tmp/ex2",
    KEY_SIZE, 4, // now the size is important
    KEY_VALUE, "some data", // sets the binary value ("some")
    KEY_END); // end of args
  • KEY_CASCADING_NAME allow the name to start with / useful for ksLookup() and kdbGet() parent/lookup keys
  • KEY_META_NAME allow the name to start with arbitrary namespaces useful to compare with metakeys
Deprecated:
The flags below are deprecated and KEY_META should be preferred. They remain some time, however, for compatibility:
Parameters
namea valid name to the key, or NULL to get a simple initialized, but really empty, object
See also
keyDel()
Returns
a pointer to a new allocated and initialized Key object.
Return values
NULLon allocation error or if an invalid name was passed (see keySetName()).