Doubly linked list implementation in C

linked-lists.c

/*
 * An implementation of doubly linked lists in C.
 *
 * API:
 *  * init()
 *      Initializes a doubly linked list and returns it.
 *  * push( list, value )
 *      Appends a new element with value to the list.
 *  * destroy( list, value )
 *      Destroys the first element with value found in the list.
 *  * print( list )
 *      Prints a linear representation of the list.
 *  * remove( list, element )
 *      Remove element from list and free it.
 *  * find( list, value )
 *      Finds the first element in list with value.
 *  * remove_by_value( list, value )
 *      Destroy first element of list with value.
 *  * pop( list )
 *      Pop the last element of the list.
 *  * shift( list )
 *      Pop the first element of the list and return it.
 *  * unshift( list, value )
 *      Prepend value to the list.
 */
#include <stdio.h>
#include <stdlib.h>

struct list_f {
    struct list_f *l_next;
    struct list_f *l_prev;
    int l_value;
};

/* Functions */
struct list_f* init();
void push( struct list_f *list, int value );
void delete( struct list_f *list, struct list_f *rem );
struct list_f* find( struct list_f *list, int value );
void remove_by_value( struct list_f *list, int value );
void pop( struct list_f *list );
int shift( struct list_f *list );
void unshift( struct list_f *list, int value );
void print( struct list_f *list );

struct list_f* init() {
    struct list_f *ret;

    ret = ( struct list_f* )malloc( sizeof( *ret ) );
    ret->l_next = ret;
    ret->l_prev = ret;
    ret->l_value = 0;

    return ret;
}

void push( struct list_f *list, int value ) {
    struct list_f *element;
    struct list_f *tail = list->l_prev;

    element = ( struct list_f* )malloc( sizeof( *element ) );
    element->l_next = list;
    element->l_prev = tail;
    element->l_value = value;
    tail->l_next = element;
    list->l_prev = element;
}

void delete( struct list_f *list, struct list_f *rem ) {
    rem->l_prev->l_next = rem->l_next;
    rem->l_next->l_prev = rem->l_prev;
}

struct list_f* find( struct list_f *list, int value ) {
    struct list_f *r;
    for ( r = list->l_next; r != list; r = r->l_next ) {
        if ( r->l_value == value ) {
            return r;
        }
    }
    return NULL;
}

void remove_by_value( struct list_f *list, int value ) {
    struct list_f* f = find( list, value );
    if ( f == NULL ) {
        return;
    }
    delete( list, f );
}

void pop( struct list_f *list ) {
    delete( list, list->l_prev );
}

int shift( struct list_f *list ) {
    int ret = list->l_next->l_value;
    delete( list, list->l_next );

    return ret;
}

void unshift( struct list_f *list, int value ) {
    struct list_f *prep;
    prep = ( struct list_f* )malloc( sizeof( *prep ) );
    prep->l_value = value;
    prep->l_prev = list;
    prep->l_next = list->l_next;
    list->l_next = prep;
    list->l_next->l_prev = prep;
}

void print( struct list_f *list ) {
    struct list_f *l;
    for ( l = list->l_next; l != list; l = l->l_next ) {
        printf( "%d ", l->l_value );
    }
    putchar( '\n' );
}

int main() {
    return 0;
}

Hi!

1. You allocate pointer size space but you need space for struct.
   ret = ( struct list_f* )malloc( sizeof( *ret ) );
2. You dont free memory after delete element from list