Functions | |
Key * | keyNew (const char *keyName,...) |
Key * | keyDup (const Key *source) |
int | keyCopy (Key *dest, const Key *source) |
int | keyDel (Key *key) |
ssize_t | keyIncRef (Key *key) |
ssize_t | keyDecRef (Key *key) |
ssize_t | keyGetRef (const Key *key) |
To use them:
#include <kdb.h>
A Key is the essential class that encapsulates key name , value and metainfo . Key properties are:
Described here the methods to allocate and free the key.
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:
int h (Key *k) { // receive key c keyCopy (k, c); // the caller will see the changed key k }
The reference counter will not change for the destination key. Affiliation to keysets are also not affected.
When you pass a NULL-pointer as source the data of dest will be cleaned completely and you get a fresh dest key.
int g (Key *k) { keyCopy (k, 0); // k is now an empty and fresh key }
dest | the key which will be written to | |
source | the key which should be copied or NULL to clean the destination key |
0 when dest was cleaned
1 when source was successfully copied
ssize_t keyDecRef | ( | Key * | key | ) |
Decrement the viability of a key object.
The reference counter can't be decremented once it reached 0. In that situation nothing will happen and 0 will be returned.
-1 on null pointer
0 when the key is ready to be freed
key | the key object to work with |
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.
key | the key object to delete |
0 when the key was freed
-1 on 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.
int f (const Key * source) { Key * dup = keyDup (source); // work with duplicate keyDel (dup); // everything related to dup is freed // and source is unchanged }
Like for a new key after keyNew() a subsequent ksAppend() makes a KeySet to take care of the lifecycle of the key.
int g (const Key * source, KeySet * ks) { Key * dup = keyDup (source); // work with duplicate ksAppendKey (ks, dup); // ksDel(ks) will also free the duplicate // source remains unchanged. }
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.
source | has to be an initializised source Key |
a fully copy of source on success
keyClear(), keyNew()
ssize_t keyGetRef | ( | const Key * | key | ) |
Return how many references the key has.
The references will be incremented when ksAppendKey() or ksAppend() uses the key and will be decremented when ksPop() is used.
keyDup() will reset the references for dupped key.
For your own applications you can use keyIncRef() and keyDelRef() for reference counting. Keys with zero references will be deleted when using keyDel().
key | the key object to work with |
-1 on null pointer
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().
Key *k; keyInc (k); function_that_keyDec(k); // work with k keyDel (k); // now really free it
The reference counter can't be incremented once it reached SSIZE_MAX. In that situation nothing will happen and SSIZE_MAX will be returned.
-1 on null pointer
SSIZE_MAX when maximum exceeded
key | the key object to work with |
Key* keyNew | ( | const char * | keyName, | |
... | ||||
) |
A practical way to fully create a Key object in one step.
This function tries to mimic the C++ way for constructors.
To just get a key object, simple do:
If you want the key object to contain a name, value, comment and other meta info read on.
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. See http://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html#AEN135You can call it in many different ways depending on the attribute tags you pass as parameters. Tags are represented as the keyswitch_t values, and tell keyNew() which Key attribute comes next.
The simplest and minimum way to use it is with no tags, only a key name:
Key *nullKey,*emptyNamedKey; // Create a key that has no name, is completely empty, but is initialized nullKey=keyNew(0); keyDel (nullKey); // Is the same as above nullKey=keyNew("", KEY_END); keyDel (nullKey); // Create and initialize a key with a name and nothing else emptyNamedKey=keyNew("user/some/example",KEY_END); keyDel (emptyNamedKey);
keyNew() allocates memory for a key object and cleans everything up. After that, it processes the given argument list.
The Key attribute tags are the following:
keyswitch_t::KEY_GID
keyName
is 0.
KeySet *ks=ksNew(0); ksAppendKey(ks,keyNew(0)); // an empty key ksAppendKey(ks,keyNew("user/sw", // the name of the key KEY_END)); // no more args ksAppendKey(ks,keyNew("user/tmp/ex1", KEY_VALUE,"some data", // set a string value KEY_END)); // end of args ksAppendKey(ks,keyNew("user/tmp/ex2", KEY_VALUE,"some data", // with a simple value KEY_MODE,0777, // permissions KEY_END)); // end of args ksAppendKey(ks,keyNew("user/tmp/ex4", KEY_TYPE,KEY_TYPE_BINARY, // key type KEY_SIZE,7, // assume binary length 7 KEY_VALUE,"some data", // value that will be truncated in 7 bytes KEY_COMMENT,"value is truncated", KEY_OWNER,"root", // owner (not uid) is root KEY_UID,0, // root uid KEY_END)); // end of args ksAppendKey(ks,keyNew("user/tmp/ex5", KEY_TYPE, KEY_TYPE_DIR | KEY_TYPE_BINARY,// dir key with a binary value KEY_SIZE,7, KEY_VALUE,"some data", // value that will be truncated in 7 bytes KEY_COMMENT,"value is truncated", KEY_OWNER,"root", // owner (not uid) is root KEY_UID,0, // root uid KEY_END)); // end of args ksDel(ks);
Key *k = keyNew(0); // ref counter 0 ksAppendKey(ks, k); // ref counter of key 1 ksDel(ks); // key will be deleted with keyset *
If you increment only by one with keyInc() the same as said above is valid:
Key *k = keyNew(0); // ref counter 0 keyIncRef(k); // ref counter of key 1 keyDel(k); // has no effect keyDecRef(k); // ref counter back to 0 keyDel(k); // key is now deleted *
If you add the key to more keySets:
Key *k = keyNew(0); // ref counter 0 ksAppendKey(ks1, k); // ref counter of key 1 ksAppendKey(ks2, k); // ref counter of key 2 ksDel(ks1); // ref counter of key 1 ksDel(ks2); // k is now deleted *
or use keyInc() 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 *
they key won't be deleted by a keyDel() as long refcounter is not 0.
The key's sync bit will always be set for any call, except:
Key *k = keyNew(0); // keyNeedSync() will be false
keyName | a valid name to the key, or NULL to get a simple initialized, but really empty, object |
keyName
was passed (see keySetName()).