lr.c

#include <stdio.h>  /* fopen, fgetc, fputs, fwrite */
#include <stdlib.h> /* exit, malloc, realloc, free */

#include "lr.h"

struct line_reader_t {
  /* All members are private. */
  FILE *f;
  char *buf;
  size_t siz;
};

line_reader_t *lr_new() {
  return (line_reader_t *)malloc(sizeof(line_reader_t));
}

/*
 * Initializes a line reader _lr_ for the stream _f_.
 */
void lr_init(line_reader_t *lr, FILE *f) {
  lr->f = f;
  lr->buf = NULL;
  lr->siz = 0;
}

/*
 * Read a file line by line.
 * http://rosettacode.org/wiki/Read_a_file_line_by_line
 *
 * Reads the next line. If successful, returns a pointer to the line,
 * and sets *len to the number of characters, at least 1. The result is
 * _not_ a C string; it has no terminating '\0'. The returned pointer
 * remains valid until the next call to lr_next() or lr_free() with
 * the same _lr_.
 *
 * next_line() returns NULL at end of file, or if there is an error (on
 * the stream, or with memory allocation).
 */
char *lr_next(line_reader_t *lr, size_t *len) {
  size_t newsiz;
  int c;
  char *newbuf;

  *len = 0; /* Start with empty line. */
  while (1) {
    c = fgetc(lr->f); /* Read next character. */
    if (ferror(lr->f)) {
      return NULL;
    }

    if (c == EOF) {
      /*
       * End of file is also end of last line,
`	 * unless this last line would be empty.
       */
      if (*len == 0) {
        return NULL;
      } else {
        return lr->buf;
      }
    } else {
      /* Append c to the buffer. */
      if (*len == lr->siz) {
        /* Need a bigger buffer! */
        newsiz = lr->siz + 4096;
        newbuf = realloc(lr->buf, newsiz);
        if (newbuf == NULL) {
          return NULL;
        }
        lr->buf = newbuf;
        lr->siz = newsiz;
      }
      lr->buf[(*len)++] = c;

      /* '\n' is end of line. */
      if (c == '\n') {
        return lr->buf;
      }
    }
  }
}

/*
 * Frees internal memory used by _lr_.
 */
void lr_free(line_reader_t *lr) {
  free(lr->buf);
  lr->buf = NULL;
  lr->siz = 0;
}