Iterator for C

iteratordemo.c

/**
 * Learning Abstraction With C
 * 
 * make with: cc     iteratordemo.c   -o iteratordemo -g
 * 
 * works as ./iteratordemo, doesnt work as: 
 * $ valgrind --leak-check=full ./iteratordemo
 */

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

typedef char *(iterator_function)(void);

char *stdin_line(void);
char *stdin_line(void) {
  int c, result_size = 0;
  char *result;
  
  result = malloc(1);

  while (1) {
    c = getchar();
    if (c == '\0' || c == EOF || c == '\n') break;
    result[result_size] = c;
    result = realloc(result, ++result_size);
  }
  
  result[result_size] = '\0';
  return result;
}

char *adjacent_file_line(void);
FILE *adjacent_file_line_file;
char *adjacent_file_line(void) {
  int c, result_size = 0;
  char *result;
  
  result = malloc(1);
  if (!adjacent_file_line_file) { result[0] = '\0'; return result; }

  while (1) {
    c = fgetc(adjacent_file_line_file);
    if (c == '\0' || c == EOF || c == '\n') break;
    result[result_size] = c;
    result = realloc(result, ++result_size);
  }
  
  result[result_size] = '\0';
  return result;
}

void printNLines(iterator_function, int);
void printNLines(iterator_function next, int count) {
  char *response;
  for (int i = 0; i < count; ++i) {
    response = next();
    printf("%s\n", response);
    free(response);
  }
}


int main(int argc, char const *argv[])
{
  /* in the future, could switch on argc/v */
  // printNLines(stdin_line, 3);

  adjacent_file_line_file = fopen("./adjacent_file", "r");
  printNLines(adjacent_file_line, 3);
  fclose(adjacent_file_line_file);
  adjacent_file_line_file = NULL;
  
  return 0;
}