Using fgets to get lines of text from a file and store them into an array

I am struggling to get lines of text from a file and storing them into an array. I have used a debugger on my code and it seems to get the first couple lines of text but then there is a segmentation fault when it gets to the third line of text. I believe there is something wrong with my allocate_mem() function because the fault occurs when it is called during the 3rd iteration of the while loop in read_lines(). Help would be much appreciated!

My Code:

#include <stdio.h>  #include <stdlib.h>    char* read_one_line(FILE* fp, char* line);  char* allocate_mem(FILE* fp, char* line);    void print_lines(char** lines, int num_lines){      int i;      for(i = 0 ; i < num_lines; ++i){          printf("%d. %s", i+1, lines[i]);      }  }    void free_lines(char** lines, int num_lines){      int i;        for(i = 0 ; i < num_lines; ++i){          free(lines[i]);      }        if(lines != NULL && num_lines > 0){          free(lines);      }  }    FILE* validate_input(int argc, char* argv[]){        FILE* fp = NULL;        if(argc < 2){          printf("Not enough arguments entered.\nEnding program.\n");          exit(0);      }      else if(argc > 2){          printf("Too many arguments entered.\nEnding program.\n");          exit(0);      }        fp = fopen(argv[1], "r");        if(fp == NULL){          printf("Unable to open file: %s\nEnding program.\n", argv[1]);          exit(0);      }      return fp;  }    void read_lines(FILE* fp, char*** lines, int* num_lines) {    *num_lines = 0;    long length = 0;    do {      *num_lines += 1;      *lines = realloc(*lines, *num_lines * sizeof(*lines));      *lines[*num_lines - 1] = allocate_mem(fp, *lines[*num_lines - 1], &length);      *lines[*num_lines - 1] = read_one_line(fp, *lines[*num_lines - 1], &length);    } while(read_one_line(fp, *lines[*num_lines - 1], &length) != NULL);  }    char* read_one_line(FILE* fp, char* line, long* length) {    fgets(line, *length, fp);    return line;  }    char* allocate_mem(FILE* fp, char* line, long* length) {    fseek(fp, 0, SEEK_END);    *length = ftell(fp);    fseek(fp, 0, SEEK_SET);    line = malloc((*length + 1) * sizeof(char));    return line;  }    int main(int argc, char* argv[]){      char** lines = NULL;      int num_lines = 0;      FILE* fp = validate_input(argc, argv);        read_lines(fp, &lines, &num_lines);      print_lines(lines, num_lines);      free_lines(lines, num_lines);      fclose(fp);        return 0;  }  

https://stackoverflow.com/questions/66592372/using-fgets-to-get-lines-of-text-from-a-file-and-store-them-into-an-array March 12, 2021 at 08:10AM