Strings.

Pointers to strings.

C does not have a "string" datatype. To create a string you have to use a char array or a char pointer. If you are not familur with char arrays I recomend that you read about them now.

To recap, a char pointer is defined like this:

main() { char *Text; }

All this program does is reserve storage that will hold an address. At this point the address could be anything. To initalize Text you can code:

main() { char *Text = "Thunder"; }

Text now has the address of the first character in Thunder. Graphically, things look like this.

      (Address) (Data)
      
           ---- ----    
          | F1 | 00 <------- Text |----|----| (Data) (Adress) | F2 | 00 | ------------- |----|----| -------> 54 (T) | D1 |
	  | F3 | 00 |        |       |--------|----|
	  |----|----|  *Text |       | 68 (h) | D2 |
	  | F4 | D1 | -------        |--------|----|
	   ---------                 | 75 (u) | D3 |
	                             |--------|----|
				     | 6E (n) | D4 |
				     |--------|----|
                                     | 64 (d) | D5 |
                                     |--------|----|
                                     | 65 (e) | D6 |
                                     |--------|----|
                                     | 72 (r) | D7 |
                                     |--------|----|     
                                     | 00     | D8 |
                                      -------------

Please note the 00 at the end of Thunder. This is the NULL character and is used to mark the end of a string.

If we wanted to O/P the data pointed to by a char pointer we can code.

Source

main() { char *Text1 = "Thunder"; /* Define and initalize */ char *Text2; /* Define only */ Text2 = "Bird"; /* Point to some text */ printf("%s%s\n", Text1, Text2); }

Result

ThunderBird

This is all very well, but there is a MAJOR problem! Thunder and Bird are constants, they cannot be changed in anyway. We need a method of pointing to some storage that can be altered and true to form, C provides a function called malloc to do just that.

See Also:

VOID keyword.