read_input.c

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

static char *read_stdin(void)
{
  size_t cap = 4096, /* Initial capacity for the char buffer */
      len = 0;       /* Current offset of the buffer */

  char *buffer = malloc(cap * sizeof(char));
  int c;

  /* Read char by char, breaking if we reach EOF or a newline */
  while ((c = fgetc(stdin)) != '\n' && !feof(stdin))
  {
    buffer[len] = c;

    /* When cap == len, we need to resize the buffer
       * so that we don't overwrite any bytes
       */
    if (++len == cap)
    {
      /* Make the output buffer twice its current size */
      buffer = realloc(buffer, (cap *= 2) * sizeof(char));
    }
  }

  /* If EOF, clear stdin error for future readings */
  if (c == EOF)
  {
    clearerr(stdin);
  }

  /* Trim off any unused bytes from the buffer */
  buffer = realloc(buffer, (len + 1) * sizeof(char));

  /* Pad the last byte so we don't overread the buffer in the future */
  buffer[len] = '\0';

  return buffer;
}

static char *read_stdin_str(const char *message) {
  printf("%s", message);
  return read_stdin();
}

int read_stdin_int(const char *message, const char *invalid_message)
{
  int n;

  printf("%s", message);
  char *input = read_stdin();

  while (sscanf(input, "%d", &n) != 1)
  {
    printf("%s", invalid_message);
    printf("%s", message);

    free(input);
    input = read_stdin();
  }

  free(input);

  return n;
}

float read_stdin_float(const char *message, const char *invalid_message)
{
  float n;

  printf("%s", message);
  char *input = read_stdin();

  while (sscanf(input, "%f", &n) != 1)
  {
    printf("%s", invalid_message);
    printf("%s", message);

    free(input);
    input = read_stdin();
  }

  free(input);

  return n;
}

double read_stdin_double(const char *message, const char *invalid_message)
{
  double n;

  printf("%s", message);
  char *input = read_stdin();

  while (sscanf(input, "%lf", &n) != 1)
  {
    printf("%s", invalid_message);
    printf("%s", message);

    free(input);
    input = read_stdin();
  }

  free(input);

  return n;
}