DAOK - generalized trim f(x)'s

[jim mcnamara]

/*
// General trim function(s)
// generalize the functions to remove white space
// make the VALUE macro t use is_ctrl and is_space
// for spaces only use is_space
*/
#define _IS_SP	1			/* is space */
#define _IS_CTL	32			/* Control */
extern	char _Cdecl _ctype[];	 /* Character type array */

/*                       is_ctrl() macro          is_space() macro   */
#define VALUE(c)  (_ctype[(c) + 1] & _IS_CTL)|(_ctype[(c) + 1] & _IS_SP)

char *ltrim(char *s)
{
     int set=0;
     char *buf;
     char *keep;
     if(*s==0x00) return s; /* exit early */
     buf=s,keep=s;
     while ( VALUE(*buf) ) buf++,set++;
     if(set){        /* make shortened s start at a new beginning */
       while (*buf!=0x00)*keep++=*buf++;
       *keep=0x00;
     }
     return s;
}

char *rtrim(char *s)
{
   char *buf;
   if(*s==0x00) return s; /* exit early */
   buf=s;
   buf+=strlen(buf)-1;
   while(VALUE(*buf) )*buf--=0x00;     /* shorten s  */
   return s;
}

char *trim(char *s)
{
   if(*s==0x00) return s; /* exit early */
   return ltrim( rtrim(s) ); /* trim = remove blanks both ends */
}

[Daok]

I had just take an eye on your code and wow, it's very complex. Can you tell me why you use HEXadecimal number? 0x00 ?

[Daok]

And I do not understand that :

extern	char _Cdecl _ctype[];	 /* Character type array */

/*                       is_ctrl() macro          is_space() macro   */
#define VALUE(c)  (_ctype[(c) + 1] & _IS_CTL)|(_ctype[(c) + 1] & _IS_SP)

[jim mcnamara]

0x00 marks the end of a C string. You know that you have reached string end of a string when you hit a 0x00 character.

extern	char _Cdecl _ctype[];	 /* Character type array */

Compilers create stuff in the background that you may not know about. This is one of those things - an array of char that is used by ctype operations - operations that work with individual characters.

extern means the variable is defined somewhere else. But we use it here, too.

#define VALUE(c)  (_ctype[(c) + 1] & _IS_CTL)|(_ctype[(c) + 1] & _IS_SP)

This is just a macro. It tells you if the current character is a control character or a space. Control characters and spaces together make up the "white" space in text.

You could change it to find only spaces like this:

#define VALUE(c)  (_ctype[(c) + 1] & _IS_SP)

That's why macros are nice - they let you make a change in one place, and it spreads throughout all of the code.

Do you see now what the code does? It looks complex but it is very simple, really.