Trouble dynamically allocating memory for string array - c

Question

I am trying to write a function that reads a text file and copies each line of the text file into a line of an array that is passed into the function.
void read_lines(FILE* fp, char*** lines, int* num_lines) {
int i = 0, line_count = 0;
char line[256], c;
fscanf(fp, "%c", &c);
while(!feof(fp)){
if(c == '\n') {
++line_count;
}
printf("%c", c);
fscanf(fp, "%c", &c);
}
rewind(fp);
*num_lines = line_count;
lines = (char***)malloc(line_count * sizeof(char**));
while (fgets(line, sizeof(line), fp) != NULL) {
lines[i] = (char**)malloc(strlen(line) * sizeof(char*));
strcpy(*lines[i], line);
}
++i;
}
}
The initial part scans for newlines so that I know how much to allocate to lines initially. I am not sure where I am going wrong.
Additionally, if anybody has any resources that could help me to better understand how to dynamically allocate space, that would be greatly appreciated.

Answer 1

You should understand how the pointers work. After that, dynamical memory allocation task would be pretty trivial. Right now your code is completely wrong:
//here you assign to the argument. While this is technically allowed
//it is most certainly not what you have intended
lines = (char***)malloc(line_count * sizeof(char**));
while (fgets(line, sizeof(line), fp) != NULL) {
//sizeof(char*) <> sizeof(char). Also you need a space for the trailing \0
lines[i] = (char**)malloc(strlen(line) * sizeof(char*));
//[] precedes * so it is copying the string somewhere you not intend to
strcpy(*lines[i], line);
}
++i;
}
Correct version should be:
*lines = malloc(line_count * sizeof(char*));
while (fgets(line, sizeof(line), fp) != NULL) {
(*lines)[i] = malloc((strlen(line) + 1) * sizeof(char));
strcpy((*lines)[i], line);
}
++i;
}
Note, that you need to use (*lines)[i] construct, because [] operator precedes * (dereference) operator.

Answer 2

Code is making various mistakes including the key ones detailed by #Ari0nhh
The other is the counting the '\n' can fail to get the correct number of lines vs. fgets() in 3 ways:
Line exceeds 256.
More than INT_MAX lines.
Last line does not end with a '\n'.
Suggest instead use the same loop to count "lines"
unsigned long long line_count = 0;
while (fgets(line, sizeof(line), fp) != NULL) {
line_count++;
}
rewind(fp);
....
assert(line_count <= SIZE_MAX/sizeof *(*lines));
*lines = malloc(sizeof *(*lines) * line_count);