Question

I’m currently writing a parser for my toy language, and as a part of that parser i have written print function that well… basically prints its argument. For string constant all it does is

printf("%s", pointer);

so

print("\n")

should be executed as

printf("%s", ptr_to_loaded_string);

(more or less)

However, my current problem is, that C escapes special character sequences while reading script file. So instead of “\n” I get “\\n”.

My question is: is there some way I can avoid the escaping of this sequences, and if not what’s the best way to deal with them? I’m currently thinking about search and replace – replace each sequence of 2 ‘\’ with one ‘\’, but it may be a little problematic (string length change, reallocing, etc.) – i want to avoid that solution unless it’s absolutely necessary.

edit: argh, stackoverflow escaped my example….

Answer 1

It’s not that C is un-escaping your sequences — it’s that it’s simply leaving them alone, so your “\n” in the input stream is read as two characters (‘\’ and ‘n’).

Here’s some code I wrote years ago to deal with this:

/*
** Public Domain by Jerry Coffin.
**
** Interpets a string in a manner similar to that the compiler
** does string literals in a program.  All escape sequences are
** longer than their translated equivalant, so the string is
** translated in place and either remains the same length or
** becomes shorter.
*/

#include <string.h>
#include <stdio.h>
#include "snip_str.h"

char *translate(char *string)
{
      char *here=string;
      size_t len=strlen(string);
      int num;
      int numlen;

      while (NULL!=(here=strchr(here,'\\')))
      {
            numlen=1;
            switch (here[1])
            {
            case '\\':
                  break;

            case 'r':
                  *here = '\r';
                  break;

            case 'n':
                  *here = '\n';
                  break;

            case 't':
                  *here = '\t';
                  break;

            case 'v':
                  *here = '\v';
                  break;

            case 'a':
                  *here = '\a';
                  break;

            case '0':
            case '1':
            case '2':
            case '3':
            case '4':
            case '5':
            case '6':
            case '7':
                  numlen = sscanf(here,"%o",&num);
                  *here = (char)num;
                  break;

            case 'x':
                  numlen = sscanf(here,"%x",&num);
                  *here = (char) num;
                  break;
            }
            num = here - string + numlen;
            here++;
            memmove(here,here+numlen,len-num );
      }
      return string;
}