Class 35: Strings

Held: Wednesday, 6 April 2011

Summary: We begin to consider the design of strings in C.

Related Pages:

• EBoard.
• Lab: Strings.
• Reading: K&R 5.5, B3.

Notes:

• Responses to your questions on the make reading have been posted. Class time discussing them will be limited.
• Missing questions from DG, MH, JTL.
• Reading for Friday: Debugging with DDD.
• EC for today's 's M.C. Escher talk [academic]
• EC for Thursday's nonvo on Iowa Water (or other part of that symposium) [academic]
• EC for Friday's CS Table on Watson [academic]
• EC for Friday's presentation of Sita Sings the Blues [academic]
• EC for any activity in the animation festival, including Tiny Circus [peer]
• EC for either part of the baseball doubleheader against Knox [peer]

Overview:

• About strings.
• Important string functions.
• Thinking like a C programmer.
• Lab.

Strings

• In C, strings are null-terminated arrays of characters.
  • "null" means "0".
• Since arrays are (mostly) interchangable with pointers, strings are also pointers to characters.
• While this sounds simple, it's easy to screw things up.

Important String Functions

• strlen (str) - find the number of characters in str.
• strcpy (target, source) - copy string from source to target.
• strncpy (target, source, n) - copy up to n characters from source to target.
• strcat (target, source) - put source on the end of target.
• strcmp (str1, str2) - compare two strings.

Thinking Like a C Programmer

While I've put strcpy in the outline, a reading question suggests that I should do strcmp instead.

/**
 * strcpy: Copy source (s) to target (t).
 */
void 
strcpy (char *t, char *s) 
{
  char *result = t;
  while (*t++ = *s++)
    ;
  return result;
} // strcpy

Lab

• Do the lab.