Regular Expressions (Lecture 11)

Current readings King Chap. 17 or K&R Chapter 6, Structures.

The book "Your Unix" has good chapters on vi and emacs, pattern matching (Chapter 15) and regular expressions, CVS and make.

Press here for other lectures

Press here for slides #11 (postscript) regular expressions and pointers to functions (old)

Press here for basic information about Structures

Press here for next design topic from Mark Green's notes.

Preparations for C++ is also worth reading at this time.

Fun with strings

The assumption that a string ends with the null character permits writing very concise programs for manipulation of existing strings. Usually we need dynamic memory allocation to create room for a new string (e.g. malloc works well here).

Let us examine four ways of how we can copy strings. These functions have the following preconditions:

s (for source) is a pointer to a string,
t (for target) is a pointer to a sequence of bytes in memory not occupied by other data which is at least as long as length(s)+1.

   /* Array subscript version */
void astrcopy (char s[], char t[]) {	// or (char* s, char* t)
  int i = 0;
  while ((t[i] = s[i]) != '\0')
    i++;
}

   /* Pointer version 1 */
void p1strcopy (char* s, char* t) {
  int i = 0;
  while ((*(t+i) = *(s+i)) != '\0') 
    i++;
}

   /* Pointer version 2 */
void p2strcopy (char* s, char* t) {
  while ((*t++ = *s++) != '\0') 
    ;
}

   /* Pointer version 3 */
void p3strcopy (char* s, char* t) {
  while (*t++ = *s++)  
    ;
}