// fread example: read an entire file
// source: http://www.cplusplus.com/

// Class: this is an important snippet of code.
// In crawler you will have to read a file into
// a dynamically allocated (malloc) buffer.
// Ponder: how big should the buffer be? Well,
// at least as big as the file. How do you find
// out how big the file is? Also, remember a 
// memory string has to be terminated by a NULL.
// A file is terminated with EOF and not a NULL.
// How do you make sure that a text file copied in
// to a memory string terminates correctly?
// CLASS: that's really important.

// This little snippet answers those questions.

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

int main() {
  FILE *pFile;
  long lSize;
  char *buffer;
  size_t result;

  pFile = fopen("myfile.txt", "r");
  if (pFile==NULL){
    fputs("File error\n", stderr); 
    exit (1);
  }

  // obtain file size
  fseek(pFile, 0, SEEK_END); // seek to the end of the file
  lSize = ftell(pFile);  // get the current file pointer 
  rewind(pFile);  // rewind to the beginning of the file

  // allocate memory to contain the whole file:
  // add one more byte for the NULL character to
  // terminate the memory string

  buffer = (char *)malloc(sizeof(char)*lSize + 1);
  if (buffer == NULL) {
    fputs("Memory error", stderr); 
    exit (2);  // different error code from the earlier
               // failed to open the file - why?
  }

  // set the memory to zero before you copy in.
  // the lSize + 1 byte will be 0 which is NULL '\0'
  // note, we clear memory and add the NULL at the same time

  memset(buffer, 0, sizeof(char)*lSize + 1);

  // copy the file into the buffer:
  result = fread(buffer, sizeof(char), lSize, pFile);
  if (result != lSize) {
    fputs("Reading error", stderr); 
    exit (3); // we use different exit codes for different errrors, that's why.
  }

  // the whole file is now loaded in the memory buffer. Is it correct?
  //  
  // look at the file using the cat myfile.txt. Problem is you
  // can't see hidden whitespace characters like newline or NULL.
  // try, od -t c myfile.txt. Now you can see the complete
  // file. What is at the end of the file? Probably a \n (newline).

  // Why not run gdb and look at the buffer contents.
  // Looks good. OK.
  // Let's print it out

  fputs(buffer, stdout);
  
  // terminate

  fclose(pFile);
  free(buffer);
  return EXIT_SUCCESS;
}