DAOK - generalized trim f(x)'s

Code:

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/*
// 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 */
}

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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 ?

And I do not understand that :

Code:

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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)

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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.

Code:

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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.

Code:

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

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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:

Code:

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

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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.