Thread: Global arrays, file I/O and pointers

Hi there, I'm a programming newbie and I can't seem to get this section of code to work. I read in the lines of a file, but immediately after the loop that creates an array of the strings in the file, all char pointers point to the last item in the list.

Code:

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

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

typedef char * string;
string *dictionary;
int num_lines;


void *thread1(char *input_word){
		pthread_mutex_lock(&mutex);
		pthread_mutex_unlock(&mutex);
}

void *thread2(char *input_word){
		pthread_mutex_lock(&mutex);
		pthread_mutex_unlock(&mutex);
}


main(){	

	//count number of words in dictionary file
	FILE *input = fopen("dictionary.txt","r");
	num_lines=0;
	char temp[50];
	while (fscanf(input,"%s",temp)!=EOF) num_lines++;
	rewind(input);

	//create a 1D array containing the words from the dictionary
	dictionary=malloc(sizeof(char*)*num_lines);
	int x;
	for(x=0;x<num_lines;x++)
		dictionary[x]=malloc(sizeof(char)*20);
	num_lines=0;
	while (fscanf(input,"%s",temp)!=EOF){
		dictionary[num_lines]=temp;
		num_lines++;
                //array properly lists words here
	}

        //but out here all dictionary[x] locations contain the last line in the file.    

	//scan for the input word
	char *user_Input=NULL;
	int test;
	user_Input=malloc(sizeof(char)*20);
	while(1){
		printf("Enter a string: ");
		scanf("%s",user_Input);
		if(strcmp(user_Input,"exit")==0) break;
		pthread_t t_1,t_2;
		if(test = pthread_create(&t_1, NULL, (void *(*)(void *))thread1, user_Input))
			printf("Thread 1 creation failure.\n");
		if(test = pthread_create(&t_2, NULL, (void *(*)(void *))thread2, user_Input))
			printf("Thread 2 creation failure.\n");
		pthread_join(t_1, NULL);
		pthread_join(t_2, NULL);
	}
	free(user_Input);


}

Thanks for any advice you may have!!!

Why don't you use realloc() rather than reading file twice?

Code:

char temp[100];
for(i = 0; i < num_lines;i++) {
  fscanf(input,"%99s",temp);
  dictionary[i] = strdup( temp );
}

Code:

		dictionary[num_lines]=temp;

is Wrong. Read Question 7.4
Perhaps you are thinking = does copying ?
1st you allocate space. the pointer is pointing to that memory, later you point that pointer to temp. Thus your allocated memory is gone. you've no way to access allocated memory.(memory leak).
Correct way is to copy contents to allocated memory that pointer is pointing.

Code:

char *p = malloc( strlen(s) + 1 );      // +1 for '\0'
p = s;            // Wrong, 
strcpy(p,s);      // copy s to p, correct