Thread: Reading strings from a text file and storing into an array help!

Hey all,

I've been making a program that reads in from a .txt file which is a dictionary of one word on each line like so;

aa
aah
aahed
aahing
aahs
aal
aalii
aaliis
aals

What I want to do is read in from the text file and store each string from each line into an array and be able to call that string later on. For example with the above text calling words[1] would return "aah". Here is my code that I have so far below, at first it seems to work but it looks like it fills all of the array with the last word in the text file? Any help would be greatly appreciated!

Code:

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


int main ()
{


int dicsize = 80368;
char newword[100];
char* words[dicsize-1];


// Load Files
FILE *dict;
dict=fopen("dictionary.txt", "r");
if (dict==NULL) {
printf("Unable to open dictionary.txt\n");
} else {
// Input Dictionary
 int i = 0;
 while (fgets(newword, sizeof newword, dict) != NULL) {
 printf("%s", newword);
 words[i] = newword;
 i++;
 }
}




printf("\nTest: %s", words[2]);






return(0);
}

Why declare words to have dicsize-1 entries? Are you intentionally leaving one word out? You should also have a check in your while loop that ensures you don't enter too many words, that would create a buffer overrun.

Originally Posted by MK27

Yes, because 'words' is an array of pointers, and you pointed all of them to the same place, newword. After the loop ends, newword contains the last value that was placed into it.

You need something like:

Code:

char words[dicsize-1][100];

Then you need to

A) copy the string in newword into a place in newwords at each iteration.
or
B) just use words[i] in fgets and forget about newwords.

By "copy", I mean strcpy() or something similar. You cannot assign the content of an entire array (a string is an array of characters) with =.

Ah I understand now that at the end of the loop all of the pointers are pointing to one value(newword), this means I need to store newword into an array?

Could you explain a little bit more about how to implement the 2d array?

Thanks for your help

What don't you get? I think MK27 was quite clear. He gave you the declaration verbatim. Suggestion "B", to use words[i] as the buffer you read into with fgets also seems straight forward. Why not give it your best effort and post back if you still have trouble.

The code im trying below gives me the error Segmentation fault (core dumped);

Code:

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


int main ()
{


int dicsize = 80368;
int newword = 100;
char words[dicsize-1][100];


// Load Files
FILE *dict;
dict=fopen("dictionary.txt", "r");
if (dict==NULL) {
printf("Unable to open dictionary.txt\n");
} else {
// Input Dictionary
 int i = 0;
 while (fgets(words[i], sizeof newword, dict) != NULL) {
 i++;
 }
}


return(0);
}

Any suggestions?

Thanks

Code:

char words[dicsize-1][100];

This is rather big ( > 8 MB ) for the stack. You should dynamically allocate the array.

Code:

while (fgets(words[i], sizeof newword, dict) != NULL) {

guess you want newword instead of sizeof newword.
Kurt

You should never use VLA, VLA are bad, only C99, without error-handling and not C++ compatible.

Code:

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

#define MAXWORDNUM 90000
#define MAXWORDLEN 100

int main ()
{
char words[MAXWORDNUM][MAXWORDLEN];

FILE *dict;
dict=fopen("dictionary.txt", "r");
if (dict==NULL) {
printf("Unable to open dictionary.txt\n");
} else {
 int i = 0;
 while (i<MAXWORDNUM && fgets(words[i], MAXWORDLEN, dict) != NULL) {
  if( words[i][strlen(words[i])-1]=='\n' ) 
   words[i][strlen(words[i])-1]='\0'; /* remove a newline here */
 i++;
 }
}


return(0);
}

Right I have decided to go a different way and use structures for each word, the following code gives me the same Segmentation fault error, could anyone explain why this is happening?

Code:

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


#define maxwords 90000
#define maxwordlen 100


typedef struct words
{
char word[maxwordlen];
} words;


int main ()
{
words wordlist[maxwords];
char tempword[maxwordlen];


FILE *dict;
dict=fopen("dictionary.txt", "r");
if (dict==NULL) {
printf("Unable to open dictionary.txt\n");
} else {
 int i = 0;
 while (i<maxwords && fgets(tempword, maxwordlen, dict) != NULL) {
 fgets(wordlist[i].word, maxwordlen, dict);
 i++;
 }
}


fclose(dict);


return(0);
}

Thanks for your time

Code:

 while (i<maxwords && fgets(tempword, maxwordlen, dict) != NULL) {
 fgets(wordlist[i].word, maxwordlen, dict);
 i++;
 }

This code reads two words at a time from the file and stores each word in different locations. I don't think it should cause a segfault, but you probably want to fix that nonetheless.

Originally Posted by QuantumPete

I don't see what's so bad about variable length arrays.

Can you read?

Originally Posted by QuantumPete

And they certainly are C++ compatible.

VLA are not supported by C++98,C++03,C++11, therefore VLA are not compatible with C++.

Why does C++ compatibility matter here?