Seemingly automatic pointer freeing - c

Question

I have a function whichtakes a file, reads it line by line, puts every line in a *char[], puts this twodimensional array in a struct, and returns this struct:
wordlist.h:
#ifndef H_WORDLIST
#define H_WORDLIST
typedef struct {
char **chWordsList;
int listlen;
}Wordlist;
Wordlist getWordlistFromFile(char *chFilename);
char *getRandomWord();
#endif
The function (plus headers):
#include "wordlist.h"
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#define WORDSIZE 100
Wordlist getWordlistFromFile(char *chFilename){
FILE *file = fopen(chFilename,"r");
if (file == NULL){
printf("Unable to open file %s. Check if the file exists and can be read by this user.\n",chFilename);
exit(1);
}
char chWord[WORDSIZE];
int intFileSize = 0;
//First: coundt the amount of lines in the file
while((fgets(chWord,WORDSIZE,file) != NULL)){
++intFileSize;
}
rewind(file);
char *chWordList[intFileSize];
for (int count = 0; (fgets(chWord,WORDSIZE,file) != NULL); ++count){
chWordList[count] = malloc( strlen(chWord +1));
strcpy(chWordList[count],chWord);
chWordList[count][strlen(chWord) -1] = 0;
}
fclose(file);
Wordlist wordlist;
wordlist.chWordsList = chWordList;
wordlist.listlen = intFileSize;
for (int i = 0; i < wordlist.listlen; ++i){
printf("%s\n", wordlist.chWordsList[i]);
}
return wordlist;
}
So far this works great. The last for loop prints exactly every line of the given file, all fully expected behaviour, works perfect. Now, I actually want to use the function. So: in my main.c:
Wordlist list = getWordlistFromFile(strFilePath);
for (int i = 0; i < list.listlen; ++i){
printf("%s\n", list.chWordsList[i]);
}
This gives me the weirdest output:
abacus
wordlist
(null)
(null)
��Ⳏ
E����H�E
gasses
While the output should be:
abacus
amused
amours
arabic
cocain
cursor
gasses
It seems to me almost like some pointers get freed or something, while others stay intact. What is going on? Why is wordlist perfect before the return and broken after?

Answer 1

char *chWordList[intFileSize]
This array of strings is allocated on stack since it's declared as a local of getWordlistFromFile. Upon exiting the function the stack pointer is decreased and the array is no longer valid.
You should use the same approach used for the single string: allocate in on heap.
char **chWordList = malloc(intFileSize*sizeof(char*))
In this way the array will persist the scope of the function and you will be able to use it after the call to the function.

Answer 2

Because you are returning pointers to objects whose lifetime has expired. In particular, chWordsList inside the return value points to an object whose lifetime ends when the function returns. When you dereference that pointer you get undefined behavior (UB); therefore any result would not be surprising.
What you need to do is malloc memory for the chWordList instead of declaring it as a local array:
char **chWordList = malloc(intFileSize * sizeof(char*))

Answer 3

Change
char *chWordList[intFileSize];
to
char **chWordList = malloc(sizeof(char *) * intFileSize);
i.e allocated chwordList and set that in the WordList.
Your code is returning array variable chWordList allocated on stack, so it will not be valid once the function getWordlistFromFile() completes and returns to main().