Getting my values from a C pointer array - c

Question

Really struggling here and cannot figure out how to get my value's from an array.
I first declare this array which I want to hold a set of numbers. IDK why the size is 64, I simply am frustrated and gave it a size.
char *numberList1[64];
I then read in a file using some code I found.
FILE * fp;
char * line = NULL;
size_t len = 0;
ssize_t read;
char string[100];
int counter = 0;
printf("\n\nEnter name of File 1: ");
scanf("%s", string);
fp = fopen(string, "r");
if (fp == NULL) {
printf("invalid filename of %s",string);
exit(EXIT_FAILURE);
}
while ((read = getline(&line, &len, fp)) != -1) {
numberList1[counter] = line;
counter++;
}
Now if were to say something like printf("%s",numberList1[counter]); within the while, I would get all my numbers back.
However when I say the following, I only get the last item printed out however times there are numbers. (vectorLength).
int j;
//vectorLength is the user-entered # of lines/numbers in the file.
for (j = 0; j < vectorLength; j++) {
printf("Writing out: %s \n", numberList1[j] );
//write(pipe1[WRITE], currentNum, bitSize+1);
}
i.e. If I had numbers, 1, 2, 3, 4
I would get: 4 4 4 4
What am I doing wrong??? I have tried to find guides on understanding pointers and arrays in C but I cannot figure it out...

Answer 1

You're not preparing the parameters sent to getline() properly. According to the documentation:
If *lineptr is set to NULL and *n is set 0 before the call, then getline() will allocate a buffer for storing the line. This buffer should be freed by the user program even if getline() failed.
You want a new line buffer for each line, and you at-least-seem to want getline() to make that for you, so, after each successful read, and once you save the returned buffer pointer allocated by getline() in your array, clear the line pointer back to NULL and the length parameter back to zero:
char * line = NULL;
size_t len = 0;
while ((read = getline(&line, &len, fp)) != -1 && counter < 64)
{
numberList1[counter++] = line;
line = NULL; // <<==== ADDED
len = 0; // <<==== ADDED
}
free(line); // note: this is here because, though getline() failed, the
// documentation for the api mandates its presence.

Answer 2

I believe I've found the root of the problem.
In the code below, you are reading each line into memory at the location pointed to by line. You are then storing the pointer to the memory into each index in the array. The problem is that you are overwriting the memory at the location pointed to by line each time you read in a line. As a result, only the last-read value is stored at that location. Since each index in the array points to the same location, each iteration of the final loop in your code will display the same value.
char * line = NULL;
while ((read = getline(&line, &len, fp)) != -1) {
numberList1[counter] = line; // You are storing the pointer here, NOT the value
counter++;
}
Instead, allocate memory for the array (getline does this automatically) at each iteration of the loop and copy that pointer into the array.
while ((read = getline(&line, &len, fp)) != -1) {
numberList1[counter] = line;
line = NULL;
counter++;
}
Make sure to free all memory allocated during this process.