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# cpl_hash_set.h File Reference

`#include "cpl_port.h"`

Go to the source code of this file.

## Typedefs
typedef _CPLHashSet | CPLHashSet
typedef unsigned long(*) | CPLHashSetHashFunc (const void *elt)
typedef int(*) | CPLHashSetEqualFunc (const void *elt1, const void *elt2)
typedef void(*) | CPLHashSetFreeEltFunc (void *elt)
typedef int(*) | CPLHashSetIterEltFunc (void *elt, void *user_data)
## Functions
CPLHashSet * | CPLHashSetNew (CPLHashSetHashFunc fnHashFunc, CPLHashSetEqualFunc fnEqualFunc, CPLHashSetFreeEltFunc fnFreeEltFunc)
void | CPLHashSetDestroy (CPLHashSet *set)
int | CPLHashSetSize (const CPLHashSet *set)
void | CPLHashSetForeach (CPLHashSet *set, CPLHashSetIterEltFunc fnIterFunc, void *user_data)
int | CPLHashSetInsert (CPLHashSet *set, void *elt)
void * | CPLHashSetLookup (CPLHashSet *set, const void *elt)
int | CPLHashSetRemove (CPLHashSet *set, const void *elt)
unsigned long | CPLHashSetHashPointer (const void *elt)
int | CPLHashSetEqualPointer (const void *elt1, const void *elt2)
unsigned long | CPLHashSetHashStr (const void *pszStr)
int | CPLHashSetEqualStr (const void *pszStr1, const void *pszStr2)

## Detailed Description

Hash set implementation.

An hash set is a data structure that holds elements that are unique according to a comparison function. Operations on the hash set, such as insertion, removal or lookup, are supposed to be fast if an efficient "hash" function is provided.

## Function Documentation

void CPLHashSetDestroy | ( | CPLHashSet * | set | ) |

Destroys an allocated hash set.

This function also frees the elements if a free function was provided at the creation of the hash set.

Parameters:

  | set | the hash set

int CPLHashSetEqualPointer | ( | const void * | elt1,
|  | const void * | elt2 |
| ) |  |  |

Equality function for arbitrary pointers

Parameters:

  | elt1 | the first arbitrary pointer to compare
  | elt2 | the second arbitrary pointer to compare

Returns:
  TRUE if the pointers are equal

int CPLHashSetEqualStr | ( | const void * | elt1,
|  | const void * | elt2 |
| ) |  |  |

Equality function for strings

Parameters:

  | elt1 | the first string to compare. May be NULL.
  | elt2 | the second string to compare. May be NULL.

Returns:
  TRUE if the strings are equal

void CPLHashSetForeach | ( | CPLHashSet * | set,
|  | CPLHashSetIterEltFunc | fnIterFunc,
|  | void * | user_data |
| ) |  |  |

Walk through the hash set and runs the provided function on all the elements

This function is provided the user_data argument of CPLHashSetForeach. It must return TRUE to go on the walk through the hash set, or FALSE to make it stop.

Note : the structure of the hash set must *NOT* be modified during the walk.

Parameters:

  | set | the hash set.
  | fnIterFunc | the function called on each element.
  | user_data | the user data provided to the function.

unsigned long CPLHashSetHashPointer | ( | const void * | elt | ) |

Hash function for an arbitrary pointer

Parameters:

  | elt | the arbitrary pointer to hash

Returns:
  the hash value of the pointer

unsigned long CPLHashSetHashStr | ( | const void * | elt | ) |

Hash function for a zero-terminated string

Parameters:

  | elt | the string to hash. May be NULL.

Returns:
  the hash value of the string

int CPLHashSetInsert | ( | CPLHashSet * | set,
|  | void * | elt |
| ) |  |  |

Inserts an element into a hash set.

If the element was already inserted in the hash set, the previous element is replaced by the new element. If a free function was provided, it is used to free the previously inserted element

Parameters:

  | set | the hash set
  | elt | the new element to insert in the hash set

Returns:
  TRUE if the element was not already in the hash set

void* CPLHashSetLookup | ( | CPLHashSet * | set,
|  | const void * | elt |
| ) |  |  |

Returns the element found in the hash set corresponding to the element to look up The element must not be modified.

Parameters:

  | set | the hash set
  | elt | the element to look up in the hash set

Returns:
  the element found in the hash set or NULL

CPLHashSet* CPLHashSetNew | ( | CPLHashSetHashFunc | fnHashFunc,
|  | CPLHashSetEqualFunc | fnEqualFunc,
|  | CPLHashSetFreeEltFunc | fnFreeEltFunc |
| ) |  |  |

Creates a new hash set

The hash function must return a hash value for the elements to insert. If fnHashFunc is NULL, CPLHashSetHashPointer will be used.

The equal function must return if two elements are equal. If fnEqualFunc is NULL, CPLHashSetEqualPointer will be used.

The free function is used to free elements inserted in the hash set, when the hash set is destroyed, when elements are removed or replaced. If fnFreeEltFunc is NULL, elements inserted into the hash set will not be freed.

Parameters:

  | fnHashFunc | hash function. May be NULL.
  | fnEqualFunc | equal function. May be NULL.
  | fnFreeEltFunc | element free function. May be NULL.

Returns:
  a new hash set

int CPLHashSetRemove | ( | CPLHashSet * | set,
|  | const void * | elt |
| ) |  |  |

Removes an element from a hash set

Parameters:

  | set | the hash set
  | elt | the new element to remove from the hash set

Returns:
  TRUE if the element was in the hash set

int CPLHashSetSize | ( | const CPLHashSet * | set | ) |

Returns the number of elements inserted in the hash set

Note: this is not the internal size of the hash set

Parameters:

  | set | the hash set

Returns:
  the number of elements in the hash set

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