Why does passing char array not work but passing char* work for this:

[cedar wyvern]

static void initialize_state_id_to_token_map_for_dfa(Lexer *lexer, const char *id_to_token_type_path) {
    FILE *fp = fopen(id_to_token_type_path, "r");
    if (!fp) { report_file_error(id_to_token_type_path); }
    HashMap *string_to_token_map = lexer->string_to_token_type_map;
    int BUF_SIZE = MAX_TOKEN_SIZE;
    char buffer[BUF_SIZE];
    DFA *dfa = lexer->dfa;
    for (int i = 0; i < dfa->N_STATES; ++i) {
        fgets(buffer, BUF_SIZE, fp);
        buffer[strcspn(buffer, "\r\n")] = 0;
        // THIS LINE: &buffer does not work but changing buffer to dynamic memory         // and then doing &buffer works
        int *token = get_from_hashmap(string_to_token_map, &buffer);
        if (token == NULL) {
            fprintf(stderr, "Invalid token type %s\n", buffer);
            exit(1);
        }
        dfa->states[i].token_associated = *token;
    }
}

This is the function causing the error;

// hash function will receive pointer to string aka pointer to char*
size_t hash_string_djb2(const void *key) {
    char **str_ptr = (char **) key;
    const char *str = *str_ptr;
    size_t hash = 5381;
    int c;
    while (true) {
        c = (unsigned char) *str++;
        if (c == 0) return hash;
        hash = ((hash << 5) + hash) + c;
    }
}

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[cedar wyvern]

It works when I change the first code to:

static void initialize_state_id_to_token_map_for_dfa(Lexer *lexer, const char *id_to_token_type_path) {
    FILE *fp = fopen(id_to_token_type_path, "r");
    if (!fp) { report_file_error(id_to_token_type_path); }
    HashMap *string_to_token_map = lexer->string_to_token_type_map;
    int BUF_SIZE = MAX_TOKEN_SIZE;
    char *buffer = calloc_safe(BUF_SIZE, sizeof(char));
    DFA *dfa = lexer->dfa;
    for (int i = 0; i < dfa->N_STATES; ++i) {
        fgets(buffer, BUF_SIZE, fp);
        buffer[strcspn(buffer, "\r\n")] = 0;
        int *token = get_from_hashmap(string_to_token_map, &buffer);
        if (token == NULL) {
            fprintf(stderr, "Invalid token type %s\n", buffer);
            exit(1);
        }
        dfa->states[i].token_associated = *token;
    }
}

[primal pumice]

&buffer would give you a pointer to the array which has the same address as the first element, so it would be the same as just passing buffer into a function taking void*

[cedar wyvern]

oh

So I should do &buffer[0] right?

no

I mean, there's no way to pass address of the array? i.e. char**?

[primal pumice]

&buffer[0], buffer, and &buffer all result in a pointer represented by the same address

what does the hashmap actually store though? I'm assuming it's a hash map of char*

and so that's why the hash function would cast to char**

in that case, all of the pointers you store in the hashmap need to be dynamically allocated

[cedar wyvern]

it's a get call

so for get it doesn't matter

is there any way to pass the address of the buffer array?

[primal pumice]

if it doesn't matter, then you could pass &&*buffer or &&buffer[0]

[cedar wyvern]

okay

[primal pumice]

oh wait that doesn't work because it's a temporary pointer

so

char *str = buffer;
pass(&str);

[cedar wyvern]

okay

BTW, is storing pointers to constant memory okay in the hashmap?

Like I have constant strings array

I am storing pointers from that array in the hashmap

[primal pumice]

yeah, it's fine