I'm trying to implement a hash table in C so the idea is simple:

1- the user enters a string 2- the program adds it to the table 3- prints the whole table

but I noticed that the program replaces all previous values with the new one !! THE CODE:

//edit
//initialize array to empty string
void init(char* table[]){
    for (int i=0; i<T_LEN; i  ){
        table[i] = "";
    }
}

int hash(char* str){
    int result = 0;
    for (int i=0; i<sizeof(str); i  ){
        result  = str[i]; 
    }
    return result % T_LEN;
}

void add(char* table[]){
    char* input;
    printf("> ");
    scanf("%s", (char*)&input);
    int index = hash((char*)&input);
    table[index] = (char*)&input;
    return;
}

int main(){
    char* hash_table[T_LEN];
    init(hash_table);
    while(1){
        add(hash_table);
        print_table(hash_table);
    }
    return 0;
}

RESULT:

> abc
1         -------
2         -------
3         -------
4         -------
5         abc
6         -------
7         -------
8         -------
9         -------
10        -------
> esd
1         -------
2         -------
3         -------
4         -------
5         esd
6         -------
7         esd
8         -------
9         -------
10        -------
> ee
1         -------
2         -------
3         ee
4         -------
5         ee
6         -------
7         ee
8         -------
9         -------
10        -------

EDIT: the site says "It looks like your post is mostly code; please add some more details." so here I'm :D

CodePudding user response：

some problems with your code:

1. return; at the end of the function called add is redundant which means that it has no meaning as in all the cases the function will end at this point

2. the compiler is giving the warning while(1) in the main as you don't return from the function, so you can do

   int __attribute__((noreturn)) main()
   

to tell the compiler that the main will never return

3. in the function called init, as you are declaring an array of pointers, then it's better to write:

   table[i] = malloc(sizeof(char) * MAX_NAME_LEN);
   table[i][0] = '\0';
   

instead of:

 table[i] = "";

to reserve memory in heap for the string not in the read-only memory.

4. in the lines:

   scanf("%s", (char*)&input);
   int index = hash((char*)&input);
   

the pointer called input is already of type char*, so you don't have to cast it as it's not a better practice to cast everything, also you should reserve a space for the input variable in the heap memory like:

   char* input = malloc(sizeof(char) * MAX_NAME_LEN);  

and so your code becomes:

    char* input = malloc(sizeof(char) * MAX_NAME_LEN);
    printf("> ");
    scanf("%s", input);
    int index = hash(input);
    table[index] = input;

5. instead of sizeof() in the line:

    for (int i=0; i<sizeof(str); i  )
   

I think you should use strlen instead like:

for (int i=0; i<strlen(str); i  )

as sizeof(str) = 4 as sizeof(pointer) = 4 as the pointers has fixed size

with all this being said, this is the edited code:

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#define T_LEN 10
#define MAX_NAME_LEN    20

void print_table(char* table[])
{
    for (int i = 0; i < T_LEN;   i) {
        printf("%d\t\t%s\n",i, table[i]);
    }
}

//edit
//initialize array to empty string
void init(char* table[]){
    for (int i=0; i<T_LEN; i  ){
        table[i] = malloc(sizeof(char) * MAX_NAME_LEN);
        table[i][0] = '\0';
    }
}

int hash(char* str){
    int result = 0;
    for (int i=0; i<strlen(str); i  ){
        result  = str[i];
    }
    return result % T_LEN;
}

void add(char* table[]){
    char* input = malloc(sizeof(char) * MAX_NAME_LEN);
    printf("> ");
    scanf("%s", input);
    int index = hash(input);
    table[index] = input;
}

int __attribute__((noreturn)) main(){
    char* hash_table[T_LEN];
    init(hash_table);
    while(1){
        add(hash_table);
        print_table(hash_table);
    }
}

and this is some output:

>abc
0
1
2
3
4               abc
5
6
7
8
9
>esd
0
1
2
3
4               abc
5
6               esd
7
8
9
>ee
0
1
2               ee
3
4               abc
5
6               esd
7
8
9
>