STRINGS PART II (STRING FUNCTIONS)
				by James Tam


(You can find a version of these notes in Unix under:
/home/profs/tamj/233/examples/c_examples/string2)


The string functions that are provided with the header file string.h are described
below.  The program string_functions.c (found in the directory 
/home/profs/tamj/233/examples/c_examples/string) provides some accompanying
code.

	1) String length.
	Syntax:	strlen(string)
	
	This function will return a number that is equal to the length of
	the string in bytes which can the be stored in a variable.
	eg. - int no;
	      char string[6] = "hello";
	      no = strlen(string);
	In this example number will be equal to 5 bytes since the final null
	character at the end of the string is not counted. 


	2) String compare
		a) Compare the characters in two strings to determine
		   which one comes first alphabetically.
		Syntax: strcmp(string1,string2)
	
		This function will compare two strings and return a number
		depending if the string1 appears alphabetically before
		or after string2 (conceptually picture that it performs
		a character-by-character subtraction of string2 from string1).

		if (string1 before string2)
			strmp(string1,string2) < 0

		if (string1 after string2)
			strcmp(string1,string2) > 0

		If the strings are identical then the number 
		returned is zero. Again, like the strlen function you can 
		store the number returned in a variable.

		e.g., 	int no;
			char string1[10] = "abc";
			char string2[10] = "def";
			no = strcmp(string1,string2);
			
		In this example "no" will be a negative value since string1
		would come before string2 in the dictionary (assuming that
		both were real words).
			
		If the strings are of unequal length then the number of bytes
		that are compared is equal to the length of the shortest string.

		b) Compare only the first n characters of the strings.
		Syntax: strncmp(string1,string2,n)

		Again, this function returns a number that is the result of 
		subtracting the ASCII values of string2 from string1. If strncmp 
		reaches the end of either string after comparing "m" bytes 
		where m < n (i.e., the null character has been reached) then 
		strncmp will stop.  The determination of which string comes 
		first will be based only the first m bytes.



	3) String concatenation
		a) Append the second string onto the end of the first string.
		Syntax: strcat(string1,string2)

		It takes string2 and appends it to the end of string1.
		Then a null character is appended onto the end of the now
		lengthened string1.  The programmer is the one who must be 
		reponsible for ensuring that string1 is long enough to 
		accomodate the new characters addded on by string2 (you may 
		overwrite the memory locations that come after string1 or 
		cause a segmentation fault to oocur as your program accesses
		memory segments that it doesn't have the permission level to).

		b) Appending the first n characters of the second
		   string onto the end of the first string.
		Syntax: strncat(string1,string2,n)

		Similar to strcat but only the first n characters of string2
		are concatenated onto the end of string1.

	4) String copy 
		a) Copying string 2 into string 1 (including the 
		   null character).
		Syntax: strcpy(string1,string2)

		The contents of string2 is copied into string1 including the
		null character.  Whatever was in string1 may be lost forever.  
		Again, it is the job of the programmer to ensure that string1 is 
		long enough to hold the contents of string2.

		b) Copying the first n characters of string2 into
		   string1.		
		Syntax: strncpy(string1,string2,n)

		Copies the first n characters of string2 into string1 or until
		a null has been copied whichever comes first.  Whatever was in
		these first few characters of string1 is lost forever and the
		remainder of the string1 becomes null.