Hashes

## Hashes Hashes — Key:Value hashes or dictionaries. |

## Synopsis

    typedef     librdf_hash;
    typedef     librdf_hash_cursor;
    librdf_hash* librdf_new_hash_from_string    (librdf_world *world,
                                                 const char *name,
                                                 const char *string);
    librdf_hash* librdf_new_hash_from_array_of_strings
                                                (librdf_world *world,
                                                 const char *name,
                                                 const char **array);
    librdf_hash* librdf_new_hash_from_hash      (librdf_hash *old_hash);
    void        librdf_free_hash                (librdf_hash *hash);
    char*       librdf_hash_get                 (librdf_hash *hash,
                                                 const char *key);
    int         librdf_hash_get_as_boolean      (librdf_hash *hash,
                                                 const char *key);
    long        librdf_hash_get_as_long         (librdf_hash *hash,
                                                 const char *key);
    char*       librdf_hash_get_del             (librdf_hash *hash,
                                                 const char *key);
    int         librdf_hash_put_strings         (librdf_hash *hash,
                                                 const char *key,
                                                 const char *value);
    void        librdf_hash_print               (librdf_hash *hash,
                                                 FILE *fh);
    void        librdf_hash_print_keys          (librdf_hash *hash,
                                                 FILE *fh);
    void        librdf_hash_print_values        (librdf_hash *hash,
                                                 const char *key_string,
                                                 FILE *fh);

## Description

Interface to implementations of key:value hashes either in memory, on disk and with persistence. Keys may have multiple and duplicate values.

## Details

### librdf_hash

    typedef struct librdf_hash_s librdf_hash;

Redland hash class.

### librdf_hash_cursor

    typedef struct librdf_hash_cursor_s librdf_hash_cursor;

Redland hash cursor class.

### librdf_new_hash_from_string ()

    librdf_hash* librdf_new_hash_from_string    (librdf_world *world,
                                                 const char *name,
                                                 const char *string);

Constructor - create a new librdf_hash object from a string.

See librdf_hash_from_string for the string format.

`world` : | redland world object
`name` : | hash name
`string` : | hash encoded as a string
Returns : | a new librdf_hash object or NULL on failure

### librdf_new_hash_from_array_of_strings ()

    librdf_hash* librdf_new_hash_from_array_of_strings
                                                (librdf_world *world,
                                                 const char *name,
                                                 const char **array);

Constructor - create a new librdf_hash object from an array of strings.

`world` : | redland world object
`name` : | hash name
`array` : | address of the start of the array of char* pointers
Returns : | a new librdf_hash object or NULL on failure

### librdf_new_hash_from_hash ()

    librdf_hash* librdf_new_hash_from_hash      (librdf_hash *old_hash);

Copy Constructor - create a new librdf_hash object from an existing one.

`old_hash` : | the hash to use to construct the hash
Returns : | a new librdf_hash object or NULL on failure

### librdf_free_hash ()

    void        librdf_free_hash                (librdf_hash *hash);

Destructor - destroy a librdf_hash object.

`hash` : | hash object

### librdf_hash_get ()

    char*       librdf_hash_get                 (librdf_hash *hash,
                                                 const char *key);

Retrieve one value from hash for a given key as string.

The value returned is from newly allocated memory which the caller must free.

`hash` : | hash object
`key` : | pointer to key
Returns : | the value or NULL on failure

### librdf_hash_get_as_boolean ()

    int         librdf_hash_get_as_boolean      (librdf_hash *hash,
                                                 const char *key);

Lookup a hash key and decode value as a boolean.

`hash` : | librdf_hash object
`key` : | key string to look up
Returns : | >0 (for true), 0 (for false) or <0 (for key not found or not known boolean value)

### librdf_hash_get_as_long ()

    long        librdf_hash_get_as_long         (librdf_hash *hash,
                                                 const char *key);

Lookup a hash key and decode value as a long.

`hash` : | librdf_hash object
`key` : | key string to look up
Returns : | >0 (for success), <0 (for key not found or not known boolean value)

### librdf_hash_get_del ()

    char*       librdf_hash_get_del             (librdf_hash *hash,
                                                 const char *key);

Retrieve one value from hash for a given key as string and remove all values with that key.

The value returned is from newly allocated memory which the caller must free.

`hash` : | hash object
`key` : | pointer to key
Returns : | the value or NULL on failure

### librdf_hash_put_strings ()

    int         librdf_hash_put_strings         (librdf_hash *hash,
                                                 const char *key,
                                                 const char *value);

Insert key/value pairs into the hash as strings.

The key and values are copied into the hash, no sharing i s done.

`hash` : | hash object
`key` : | key
`value` : | value
Returns : | non 0 on failure

### librdf_hash_print ()

    void        librdf_hash_print               (librdf_hash *hash,
                                                 FILE *fh);

Pretty print the hash to a file descriptor.

`hash` : | the hash
`fh` : | file handle

### librdf_hash_print_keys ()

    void        librdf_hash_print_keys          (librdf_hash *hash,
                                                 FILE *fh);

Pretty print the keys to a file descriptor.

`hash` : | the hash
`fh` : | file handle

### librdf_hash_print_values ()

    void        librdf_hash_print_values        (librdf_hash *hash,
                                                 const char *key_string,
                                                 FILE *fh);

Pretty print the values of one key to a file descriptor.

`hash` : | the hash
`key_string` : | the key as a string
`fh` : | file handle