我开发了下面的哈希表实现代码，但是在尝试插入键值对时无法执行。
我对这个概念很陌生，并努力解决这个问题。任何帮助将不胜感激。
#include <stdlib.h>
#include <stdio.h>
#include <limits.h>
#include <string.h>
#include<conio.h>
struct entry_s {
char *key;
char *value;
struct entry_s *next;
};
typedef struct entry_s entry_t;
struct hashtable_s {
int size;
struct entry_s **table;
};
typedef struct hashtable_s hashtable_t;
/* Create a new hashtable. */
hashtable_t *ht_create( int size ) {
hashtable_t *hashtable = NULL;
int i;
if( size < 1 ) return NULL;
/* Allocate the table itself. */
if( ( hashtable = malloc( sizeof( hashtable_t ) ) ) == NULL ) {
return NULL;
}
/* Allocate pointers to the head nodes. */
if( ( hashtable->table = malloc( sizeof( entry_t * ) * size ) ) == NULL ) {
return NULL;
}
for( i = 0; i < size; i++ ) {
hashtable->table[i] = NULL;
}
hashtable->size = size;
return hashtable;
}
/* Hash a string for a particular hash table. */
int ht_hash( hashtable_t *hashtable, char *key ) {
unsigned long int hashval=0;
int i = 0;
/* Convert our string to an integer */
while( hashval < ULONG_MAX && i < strlen( key ) ) {
hashval = hashval << 8;
hashval += key[ i ];
i++;
}
return hashval % hashtable->size;
}
/* Create a key-value pair. */
entry_t *ht_newpair( char *key, char *value ) {
entry_t *newpair=NULL;
if( ( newpair == malloc( sizeof( entry_t ) ) ) == NULL ) {
return NULL;
}
if( ( newpair->key = _strdup( key ) ) == NULL ) {
return NULL;
}
if( ( newpair->value = _strdup( value ) ) == NULL ) {
return NULL;
}
newpair->next = NULL;
return newpair;
}
/* Insert a key-value pair into a hash table. */
void ht_set( hashtable_t *hashtable, char *key, char *value ) {
int bin = 0;
entry_t *newpair = NULL;
entry_t *next = NULL;
entry_t *last = NULL;
bin = ht_hash( hashtable, key );
next = hashtable->table[ bin ];
while( next != NULL && next->key != NULL && strcmp( key, next->key ) > 0 ) {
last = next;
next = next->next;
}
/* There's already a pair. Let's replace that string. */
if( next != NULL && next->key != NULL && strcmp( key, next->key ) == 0 ) {
free( next->value );
next->value = _strdup( value );
/* Nope, could't find it. Time to grow a pair. */
} else {
newpair = ht_newpair( key, value );
/* We're at the start of the linked list in this bin. */
if( next == hashtable->table[ bin ] ) {
newpair->next = next;
hashtable->table[ bin ] = newpair;
/* We're at the end of the linked list in this bin. */
} else if ( next == NULL ) {
last->next = newpair;
/* We're in the middle of the list. */
} else {
newpair->next = next;
last->next = newpair;
}
}
}
/* Retrieve a key-value pair from a hash table. */
char *ht_get( hashtable_t *hashtable, char *key ) {
int bin = 0;
entry_t *pair;
bin = ht_hash( hashtable, key );
/* Step through the bin, looking for our value. */
pair = hashtable->table[ bin ];
while( pair != NULL && pair->key != NULL && strcmp( key, pair->key ) > 0 ) {
pair = pair->next;
}
/* Did we actually find anything? */
if( pair == NULL || pair->key == NULL || strcmp( key, pair->key ) != 0 ) {
return NULL;
} else {
return pair->value;
}
}
int main( int argc, char **argv ) {
hashtable_t *hashtable = ht_create( 65536 );
ht_set( hashtable, "key1", "john" );
ht_set( hashtable, "key2", "kris" );
ht_set( hashtable, "key3", "ricky" );
ht_set( hashtable, "key4", "mike" );
printf( "%s\n", ht_get( hashtable, "key1" ) );
printf( "%s\n", ht_get( hashtable, "key2" ) );
printf( "%s\n", ht_get( hashtable, "key3" ) );
printf( "%s\n", ht_get( hashtable, "key4" ) );
return 0;
}