Singly-Linked Lists: GLib Reference Manual

## Singly-Linked Lists Singly-Linked Lists — linked lists that can be iterated in one direction |

## Functions

GSList * | g_slist_alloc ()
GSList * | g_slist_append ()
GSList * | g_slist_prepend ()
GSList * | g_slist_insert ()
GSList * | g_slist_insert_before ()
GSList * | g_slist_insert_sorted ()
GSList * | g_slist_remove ()
GSList * | g_slist_remove_link ()
GSList * | g_slist_delete_link ()
GSList * | g_slist_remove_all ()
void | g_slist_free ()
void | g_slist_free_full ()
void | g_slist_free_1 ()
guint | g_slist_length ()
GSList * | g_slist_copy ()
GSList * | g_slist_copy_deep ()
GSList * | g_slist_reverse ()
GSList * | g_slist_insert_sorted_with_data ()
GSList * | g_slist_sort ()
GSList * | g_slist_sort_with_data ()
GSList * | g_slist_concat ()
void | g_slist_foreach ()
GSList * | g_slist_last ()
#define | g_slist_next()
GSList * | g_slist_nth ()
gpointer | g_slist_nth_data ()
GSList * | g_slist_find ()
GSList * | g_slist_find_custom ()
gint | g_slist_position ()
gint | g_slist_index ()

## Types and Values

struct | GSList
#define | g_slist_free1

## Includes

    #include <gmodule.h>

## Description

The GSList structure and its associated functions provide a standard singly-linked list data structure.

Each element in the list contains a piece of data, together with a pointer which links to the next element in the list. Using this pointer it is possible to move through the list in one direction only (unlike the double-linked lists, which allow movement in both directions).

The data contained in each element can be either integer values, by using one of the Type Conversion Macros, or simply pointers to any type of data.

List elements are allocated from the slice allocator, which is more efficient than allocating elements individually.

Note that most of the GSList functions expect to be passed a pointer to the first element in the list. The functions which insert elements return the new start of the list, which may have changed.

There is no function to create a GSList. `NULL` is considered to be the empty list so you simply set a GSList* to `NULL`.

To add elements, use `g_slist_append()`, `g_slist_prepend()`, `g_slist_insert()` and `g_slist_insert_sorted()`.

To remove elements, use `g_slist_remove()`.

To find elements in the list use `g_slist_last()`, `g_slist_next()`, `g_slist_nth()`, `g_slist_nth_data()`, `g_slist_find()` and `g_slist_find_custom()`.

To find the index of an element use `g_slist_position()` and `g_slist_index()`.

To call a function for each element in the list use `g_slist_foreach()`.

To free the entire list, use `g_slist_free()`.

## Functions

### g_slist_alloc ()

    GSList *
    g_slist_alloc (void);

Allocates space for one GSList element. It is called by the `g_slist_append()`, `g_slist_prepend()`, `g_slist_insert()` and `g_slist_insert_sorted()` functions and so is rarely used on its own.

#### Returns

a pointer to the newly-allocated GSList element.

### g_slist_append ()

    GSList *
    g_slist_append (GSList *list,
                    gpointer data);

Adds a new element on to the end of the list.

The return value is the new start of the list, which may have changed, so make sure you store the new value.

Note that `g_slist_append()` has to traverse the entire list to find the end, which is inefficient when adding multiple elements. A common idiom to avoid the inefficiency is to prepend the elements and reverse the list when all elements have been added.

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    // Notice that these are initialized to the empty list.
    GSList *list = NULL, *number_list = NULL;

    // This is a list of strings.
    list = g_slist_append (list, "first");
    list = g_slist_append (list, "second");

    // This is a list of integers.
    number_list = g_slist_append (number_list, GINT_TO_POINTER (27));
    number_list = g_slist_append (number_list, GINT_TO_POINTER (14));

#### Parameters

list | a GSList |
data | the data for the new element |

#### Returns

the new start of the GSList

### g_slist_prepend ()

    GSList *
    g_slist_prepend (GSList *list,
                     gpointer data);

Adds a new element on to the start of the list.

The return value is the new start of the list, which may have changed, so make sure you store the new value.

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    // Notice that it is initialized to the empty list.
    GSList *list = NULL;
    list = g_slist_prepend (list, "last");
    list = g_slist_prepend (list, "first");

#### Parameters

list | a GSList |
data | the data for the new element |

#### Returns

the new start of the GSList

### g_slist_insert ()

    GSList *
    g_slist_insert (GSList *list,
                    gpointer data,
                    gint position);

Inserts a new element into the list at the given position.

#### Parameters

list | a GSList |
data | the data for the new element |
position | the position to insert the element. If this is negative, or is larger than the number of elements in the list, the new element is added on to the end of the list. |

#### Returns

the new start of the GSList

### g_slist_insert_before ()

    GSList *
    g_slist_insert_before (GSList *slist,
                           GSList *sibling,
                           gpointer data);

Inserts a node before `sibling` containing `data` .

#### Parameters

slist | a GSList |
sibling | node to insert `data` before |
data | data to put in the newly-inserted node |

#### Returns

the new head of the list.

### g_slist_insert_sorted ()

    GSList *
    g_slist_insert_sorted (GSList *list,
                           gpointer data,
                           GCompareFunc func);

Inserts a new element into the list, using the given comparison function to determine its position.

#### Parameters

list | a GSList |
data | the data for the new element |
func | the function to compare elements in the list. It should return a number > 0 if the first parameter comes after the second parameter in the sort order. |

#### Returns

the new start of the GSList

### g_slist_remove ()

    GSList *
    g_slist_remove (GSList *list,
                    gconstpointer data);

Removes an element from a GSList. If two elements contain the same data, only the first is removed. If none of the elements contain the data, the GSList is unchanged.

#### Parameters

list | a GSList |
data | the data of the element to remove |

#### Returns

the new start of the GSList

### g_slist_remove_link ()

    GSList *
    g_slist_remove_link (GSList *list,
                         GSList *link_);

Removes an element from a GSList, without freeing the element. The removed element's next link is set to `NULL`, so that it becomes a self-contained list with one element.

Removing arbitrary nodes from a singly-linked list requires time that is proportional to the length of the list (ie. O(n)). If you find yourself using `g_slist_remove_link()` frequently, you should consider a different data structure, such as the doubly-linked GList.

#### Parameters

list | a GSList |
link_ | an element in the GSList |

#### Returns

the new start of the GSList, without the element

### g_slist_delete_link ()

    GSList *
    g_slist_delete_link (GSList *list,
                         GSList *link_);

Removes the node link_ from the list and frees it. Compare this to `g_slist_remove_link()` which removes the node without freeing it.

Removing arbitrary nodes from a singly-linked list requires time that is proportional to the length of the list (ie. O(n)). If you find yourself using `g_slist_delete_link()` frequently, you should consider a different data structure, such as the doubly-linked GList.

#### Parameters

list | a GSList |
link_ | node to delete |

#### Returns

the new head of `list`

### g_slist_remove_all ()

    GSList *
    g_slist_remove_all (GSList *list,
                        gconstpointer data);

Removes all list nodes with data equal to `data` . Returns the new head of the list. Contrast with `g_slist_remove()` which removes only the first node matching the given data.

#### Parameters

list | a GSList |
data | data to remove |

#### Returns

new head of `list`

### g_slist_free ()

    void
    g_slist_free (GSList *list);

Frees all of the memory used by a GSList. The freed elements are returned to the slice allocator.

If list elements contain dynamically-allocated memory, you should either use `g_slist_free_full()` or free them manually first.

#### Parameters

list | a GSList |

### g_slist_free_full ()

    void
    g_slist_free_full (GSList *list,
                       GDestroyNotify free_func);

Convenience method, which frees all the memory used by a GSList, and calls the specified destroy function on every element's data.

`free_func` must not modify the list (eg, by removing the freed element from it).

#### Parameters

list | a pointer to a GSList |
free_func | the function to be called to free each element's data |

Since: 2.28

### g_slist_free_1 ()

    void
    g_slist_free_1 (GSList *list);

Frees one GSList element. It is usually used after `g_slist_remove_link()`.

#### Parameters

list | a GSList element |

### g_slist_length ()

    guint
    g_slist_length (GSList *list);

Gets the number of elements in a GSList.

This function iterates over the whole list to count its elements. To check whether the list is non-empty, it is faster to check `list` against `NULL`.

#### Parameters

list | a GSList |

#### Returns

the number of elements in the GSList

### g_slist_copy ()

    GSList *
    g_slist_copy (GSList *list);

Copies a GSList.

Note that this is a "shallow" copy. If the list elements consist of pointers to data, the pointers are copied but the actual data isn't. See `g_slist_copy_deep()` if you need to copy the data as well.

#### Parameters

list | a GSList |

#### Returns

a copy of `list`

### g_slist_copy_deep ()

    GSList *
    g_slist_copy_deep (GSList *list,
                       GCopyFunc func,
                       gpointer user_data);

Makes a full (deep) copy of a GSList.

In contrast with `g_slist_copy()`, this function uses `func` to make a copy of each list element, in addition to copying the list container itself.

`func` , as a GCopyFunc, takes two arguments, the data to be copied and a user pointer. It's safe to pass NULL as user_data, if the copy function takes only one argument.

For instance, if `list` holds a list of GObjects, you can do:

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    another_list = g_slist_copy_deep (list, (GCopyFunc) g_object_ref, NULL);

And, to entirely free the new list, you could do:

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    g_slist_free_full (another_list, g_object_unref);

#### Parameters

list | a GSList |
func | a copy function used to copy every element in the list |
user_data | user data passed to the copy function `func` , or NULL |

#### Returns

a full copy of `list` , use g_slist_free_full to free it

Since: 2.34

### g_slist_reverse ()

    GSList *
    g_slist_reverse (GSList *list);

Reverses a GSList.

#### Parameters

list | a GSList |

#### Returns

the start of the reversed GSList

### g_slist_insert_sorted_with_data ()

    GSList *
    g_slist_insert_sorted_with_data (GSList *list,
                                     gpointer data,
                                     GCompareDataFunc func,
                                     gpointer user_data);

Inserts a new element into the list, using the given comparison function to determine its position.

#### Parameters

list | a GSList |
data | the data for the new element |
func | the function to compare elements in the list. It should return a number > 0 if the first parameter comes after the second parameter in the sort order. |
user_data | data to pass to comparison function |

#### Returns

the new start of the GSList

Since: 2.10

### g_slist_sort ()

    GSList *
    g_slist_sort (GSList *list,
                  GCompareFunc compare_func);

Sorts a GSList using the given comparison function. The algorithm used is a stable sort.

#### Parameters

list | a GSList |
compare_func | the comparison function used to sort the GSList. This function is passed the data from 2 elements of the GSList and should return 0 if they are equal, a negative value if the first element comes before the second, or a positive value if the first element comes after the second. |

#### Returns

the start of the sorted GSList

### g_slist_sort_with_data ()

    GSList *
    g_slist_sort_with_data (GSList *list,
                            GCompareDataFunc compare_func,
                            gpointer user_data);

Like `g_slist_sort()`, but the sort function accepts a user data argument.

#### Parameters

list | a GSList |
compare_func | comparison function |
user_data | data to pass to comparison function |

#### Returns

new head of the list

### g_slist_concat ()

    GSList *
    g_slist_concat (GSList *list1,
                    GSList *list2);

Adds the second GSList onto the end of the first GSList. Note that the elements of the second GSList are not copied. They are used directly.

#### Parameters

list1 | a GSList |
list2 | the GSList to add to the end of the first GSList |

#### Returns

the start of the new GSList

### g_slist_foreach ()

    void
    g_slist_foreach (GSList *list,
                     GFunc func,
                     gpointer user_data);

Calls a function for each element of a GSList.

It is safe for `func` to remove the element from `list` , but it must not modify any part of the list after that element.

#### Parameters

list | a GSList |
func | the function to call with each element's data |
user_data | user data to pass to the function |

### g_slist_last ()

    GSList *
    g_slist_last (GSList *list);

Gets the last element in a GSList.

This function iterates over the whole list.

#### Parameters

list | a GSList |

#### Returns

the last element in the GSList, or `NULL` if the GSList has no elements

### g_slist_next()

    #define             g_slist_next(slist)

A convenience macro to get the next element in a GSList. Note that it is considered perfectly acceptable to access `slist->next` directly.

#### Parameters

slist | an element in a GSList. |

#### Returns

the next element, or `NULL` if there are no more elements.

### g_slist_nth ()

    GSList *
    g_slist_nth (GSList *list,
                 guint n);

Gets the element at the given position in a GSList.

#### Parameters

list | a GSList |
n | the position of the element, counting from 0 |

#### Returns

the element, or `NULL` if the position is off the end of the GSList

### g_slist_nth_data ()

    gpointer
    g_slist_nth_data (GSList *list,
                      guint n);

Gets the data of the element at the given position.

#### Parameters

list | a GSList |
n | the position of the element |

#### Returns

the element's data, or `NULL` if the position is off the end of the GSList

### g_slist_find ()

    GSList *
    g_slist_find (GSList *list,
                  gconstpointer data);

Finds the element in a GSList which contains the given data.

#### Parameters

list | a GSList |
data | the element data to find |

#### Returns

the found GSList element, or `NULL` if it is not found

### g_slist_find_custom ()

    GSList *
    g_slist_find_custom (GSList *list,
                         gconstpointer data,
                         GCompareFunc func);

Finds an element in a GSList, using a supplied function to find the desired element. It iterates over the list, calling the given function which should return 0 when the desired element is found. The function takes two gconstpointer arguments, the GSList element's data as the first argument and the given user data.

#### Parameters

list | a GSList |
data | user data passed to the function |
func | the function to call for each element. It should return 0 when the desired element is found |

#### Returns

the found GSList element, or `NULL` if it is not found

### g_slist_position ()

    gint
    g_slist_position (GSList *list,
                      GSList *llink);

Gets the position of the given element in the GSList (starting from 0).

#### Parameters

list | a GSList |
llink | an element in the GSList |

#### Returns

the position of the element in the GSList, or -1 if the element is not found

### g_slist_index ()

    gint
    g_slist_index (GSList *list,
                   gconstpointer data);

Gets the position of the element containing the given data (starting from 0).

#### Parameters

list | a GSList |
data | the data to find |

#### Returns

the index of the element containing the data, or -1 if the data is not found

## Types and Values

### struct GSList

    struct GSList {
      gpointer data;
      GSList *next;
    };

The GSList struct is used for each element in the singly-linked list.

#### Members

gpointer `data`; | holds the element's data, which can be a pointer to any kind of data, or any integer value using the Type Conversion Macros |
GSList *`next`; | contains the link to the next element in the list. |

### g_slist_free1

    #define             g_slist_free1

A macro which does the same as `g_slist_free_1()`.

Since: 2.10