Character Input

This section describes functions for performing character-oriented input. These functions are declared in the header file `stdio.h'.

These functions return an int value that is either a character of input, or the special value EOF (usually -1). It is important to store the result of these functions in a variable of type int instead of char, even when you plan to use it only as a character. Storing EOF in a char variable truncates its value to the size of a character, so that it is no longer distinguishable from the valid character `(char) -1'. So always use an int for the result of getc and friends, and check for EOF after the call; once you've verified that the result is not EOF, you can be sure that it will fit in a `char' variable without loss of information.

Function: int fgetc (FILE *stream)

This function reads the next character as an unsigned char from the stream stream and returns its value, converted to an int. If an end-of-file condition or read error occurs, EOF is returned instead.

Function: int getc (FILE *stream)

This is just like fgetc, except that it is permissible (and typical) for it to be implemented as a macro that evaluates the stream argument more than once. getc is often highly optimized, so it is usually the best function to use to read a single character.

Function: int getchar (void)

The getchar function is equivalent to getc with stdin as the value of the stream argument.

Here is an example of a function that does input using fgetc. It would work just as well using getc instead, or using getchar () instead of fgetc (stdin).

int
y_or_n_p (const char *question)
{
  fputs (question, stdout);
  while (1)
    {
      int c, answer;
      /* Write a space to separate answer from question. */
      fputc (' ', stdout);
      /* Read the first character of the line.
         This should be the answer character, but might not be. */
      c = tolower (fgetc (stdin));
      answer = c;
      /* Discard rest of input line. */
      while (c != '\n' && c != EOF)
        c = fgetc (stdin);
      /* Obey the answer if it was valid. */
      if (answer == 'y')
        return 1;
      if (answer == 'n')
        return 0;
      /* Answer was invalid: ask for valid answer. */
      fputs ("Please answer y or n:", stdout);
    }
}

Function: int getw (FILE *stream)

This function reads a word (that is, an int) from stream. It's provided for compatibility with SVID. We recommend you use fread instead (see section Block Input/Output). Unlike getc, any int value could be a valid result. getw returns EOF when it encounters end-of-file or an error, but there is no way to distinguish this from an input word with value -1.

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