"Unescaping" literal strings

[yoshiznit123]

Hi everyone,
This is my first post :-). I was wondering if there was a standard library function that converted between a literal string and its escaped C version.
For example, a function that took

\"Hey there,\" he said. \\Yo, \u4F5B.

and returned

"Hey there," he said. \Yo, 佛.

...and that could convert it back the other way, similar to a C parser. I know it would be simple to write something that does this, but getting UTF escapes would be a bigger pain. Thanks in advance,
Yoshi

[quzah]

Look up each character one at a time. If it's to be 'escaped', display its escaped form. For example, instead of printing a double quote, print a \". If you need that in a string, then you'd use this instead: \\\"

You'll need to write your own.


Quzah.

[yoshiznit123]

Thanks man, I was hoping for an equivalent of the PHP addslashes() and stripslashes(), but whatever. :-) Thanks for the quick reply. By the way, looking through the coreutils printf(1) source, found this function that does what I'm looking for (http://cvs.savannah.gnu.org/viewcvs/...s&view=markup).
Posting it here if it helps anybody else:

/* Print a \ escape sequence starting at ESCSTART.
   Return the number of characters in the escape sequence
   besides the backslash.
   If OCTAL_0 is nonzero, octal escapes are of the form \0ooo, where o
   is an octal digit; otherwise they are of the form \ooo.  */

static int
print_esc (const char *escstart, bool octal_0)
{
  const char *p = escstart + 1;
  int esc_value = 0;		/* Value of \nnn escape. */
  int esc_length;		/* Length of \nnn escape. */

  if (*p == 'x')
    {
      /* A hexadecimal \xhh escape sequence must have 1 or 2 hex. digits.  */
      for (esc_length = 0, ++p;
	   esc_length < 2 && ISXDIGIT (*p);
	   ++esc_length, ++p)
	esc_value = esc_value * 16 + hextobin (*p);
      if (esc_length == 0)
	error (EXIT_FAILURE, 0, _("missing hexadecimal number in escape"));
      putchar (esc_value);
    }
  else if (isodigit (*p))
    {
      /* Parse \0ooo (if octal_0 && *p == '0') or \ooo (otherwise).
         Allow \ooo if octal_0 && *p != '0'; this is an undocumented
         extension to POSIX that is compatible with Bash 2.05b.  */
      for (esc_length = 0, p += octal_0 && *p == '0';
	   esc_length < 3 && isodigit (*p);
	   ++esc_length, ++p)
	esc_value = esc_value * 8 + octtobin (*p);
      putchar (esc_value);
    }
  else if (*p && strchr ("\"\\abcfnrtv", *p))
    print_esc_char (*p++);
  else if (*p == 'u' || *p == 'U')
    {
      char esc_char = *p;
      unsigned int uni_value;

      uni_value = 0;
      for (esc_length = (esc_char == 'u' ? 4 : 8), ++p;
	   esc_length > 0;
	   --esc_length, ++p)
	{
	  if (!ISXDIGIT (*p))
	    error (EXIT_FAILURE, 0, _("missing hexadecimal number in escape"));
	  uni_value = uni_value * 16 + hextobin (*p);
	}

      /* A universal character name shall not specify a character short
	 identifier in the range 00000000 through 00000020, 0000007F through
	 0000009F, or 0000D800 through 0000DFFF inclusive. A universal
	 character name shall not designate a character in the required
	 character set.  */
      if ((uni_value <= 0x9f
	   && uni_value != 0x24 && uni_value != 0x40 && uni_value != 0x60)
	  || (uni_value >= 0xd800 && uni_value <= 0xdfff))
	error (EXIT_FAILURE, 0, _("invalid universal character name \\%c%0*x"),
	       esc_char, (esc_char == 'u' ? 4 : 8), uni_value);

      print_unicode_char (stdout, uni_value, 0);
    }
  else
    {
      putchar ('\\');
      if (*p)
	{
	  putchar (*p);
	  p++;
	}
    }
  return p - escstart - 1;
}

/* Print string STR, evaluating \ escapes. */

static void
print_esc_string (const char *str)
{
  for (; *str; str++)
    if (*str == '\\')
      str += print_esc (str, true);
    else
      putchar (*str);
}

Thanks alot,
Yoshi

[King Mir]

I believe sprintf() does what your looking for.

[dwks]

No, it doesn't.

char s[BUFSIZ];
sprintf(s, "\\\"Hello, World!\\\");
puts(s);

->

\"Hello, World!\"