- This wiki is out of date, use the continuation of this wiki instead
Pointer
From FenixWiki
Revision as of 02:39, 13 May 2007 (edit) Sandman (Talk | contribs) m ← Previous diff |
Current revision (23:08, 22 May 2008) (edit) (undo) Sandman (Talk | contribs) m (→Concept) |
||
(4 intermediate revisions not shown.) | |||
Line 4: | Line 4: | ||
== Definition == | == Definition == | ||
- | + | === Statement === | |
+ | Declaration of a pointer:<br> | ||
+ | <datatype> POINTER <pointername><br> | ||
+ | <datatype> * <pointername> | ||
- | '''Pointer'''s, are used to point to a location in [[memory]]. It uses 32 [[bit]]s (4 [[byte]]s) so it can map 4GB of memory into bytes. '''Pointer'''s can point to any datatype: [[int]]s, [[short]]s, [[string]]s | + | Assignment of a value to the location pointed to:<br> |
+ | POINTER <pointername> = <value>;<br> | ||
+ | <nowiki>*</nowiki> <pointername> = <value>; | ||
+ | |||
+ | === Concept === | ||
+ | '''Pointer'''s, are used to point to a location in [[memory]]. It uses 32 [[bit]]s (4 [[byte]]s) so it can map 4GB of memory into bytes. '''Pointer'''s can point to any [[datatype]]: [[int]]s, [[short]]s, [[string]]s or even usermade datatypes. | ||
+ | However, using a <code>struct pointer my_pointer</code> is pointless, because the compiler has no knowledge of the elements inside the struct pointing to, since it doesn't know which struct is meant, so this is invalid. <code>MyStruct pointer my_pointer</code>, where MyStruct is an existing struct, is also not valid, because MyStruct is not a datatype. The only way to have something like a <code>struct pointer my_pointer</code> is to use [[Type]] as seen in the example. | ||
== Example == | == Example == | ||
<pre> | <pre> | ||
- | + | ||
+ | Type _point | ||
+ | int x; | ||
+ | int y; | ||
+ | End | ||
+ | |||
+ | Type _person | ||
+ | string name; | ||
+ | int age; | ||
+ | End | ||
+ | |||
+ | Global | ||
+ | _person Person; | ||
+ | End | ||
+ | |||
+ | Process Main() | ||
Private | Private | ||
int my_int; | int my_int; | ||
- | int | + | int* my_int_pointer; |
+ | _point myPoint; | ||
+ | _person* personPointer; // possible, because _person is infact a datatype | ||
+ | //Person* personPointer; // not possible, because Person is not a datatype | ||
Begin | Begin | ||
Line 26: | Line 53: | ||
say(*my_int_pointer); | say(*my_int_pointer); | ||
- | | + | setXY(&myPoint); |
+ | say(myPoint.x); | ||
+ | say(myPoint.y); | ||
+ | |||
+ | personPointer = &Person; | ||
+ | personPointer.name = "Mies"; | ||
+ | say(Person.name); | ||
+ | say(personPointer.name); | ||
+ | |||
+ | Repeat | ||
frame; | frame; | ||
- | End | + | Until(key(_esc)) |
+ | |||
+ | End | ||
+ | |||
+ | Function int setXY(_point* p) | ||
+ | Begin | ||
+ | p.x = 3; // this is actually (*p).x = 3, but . can be used like this | ||
+ | p.y = 5; // this is actually (*p).y = 5, but . can be used like this | ||
+ | return 0; | ||
End | End | ||
</pre> | </pre> | ||
- | The & (offset) operator, when used with pointers, returns a [[void]] pointer to a variable. In the example it returns an int pointer to the variable my_int. The * (pointer) operator, when used with pointers, makes it so the pointer variable is not accessed, but the variable it's pointing to. In the example it changes access from my_int_pointer to my_int. | + | Used in example: [[say]](), [[key]](), [[Type]], [[Global]], [[Private]], [[point]] |
+ | |||
+ | The & (offset) operator, when used with pointers, returns a [[void]] pointer to a variable. In the example it returns an [[int]] pointer to the variable my_int. The * (pointer) operator, when used with pointers, makes it so the pointer variable is not accessed, but the variable it's pointing to. In the example it changes access from my_int_pointer to my_int. |
Current revision
Contents |
[edit] Definition
[edit] Statement
Declaration of a pointer:
<datatype> POINTER <pointername>
<datatype> * <pointername>
Assignment of a value to the location pointed to:
POINTER <pointername> = <value>;
* <pointername> = <value>;
[edit] Concept
Pointers, are used to point to a location in memory. It uses 32 bits (4 bytes) so it can map 4GB of memory into bytes. Pointers can point to any datatype: ints, shorts, strings or even usermade datatypes.
However, using a struct pointer my_pointer
is pointless, because the compiler has no knowledge of the elements inside the struct pointing to, since it doesn't know which struct is meant, so this is invalid. MyStruct pointer my_pointer
, where MyStruct is an existing struct, is also not valid, because MyStruct is not a datatype. The only way to have something like a struct pointer my_pointer
is to use Type as seen in the example.
[edit] Example
Type _point int x; int y; End Type _person string name; int age; End Global _person Person; End Process Main() Private int my_int; int* my_int_pointer; _point myPoint; _person* personPointer; // possible, because _person is infact a datatype //Person* personPointer; // not possible, because Person is not a datatype Begin my_int_pointer = &my_int; my_int = 3; say(my_int); say(*my_int_pointer); *my_int_pointer = 4; say(my_int); say(*my_int_pointer); setXY(&myPoint); say(myPoint.x); say(myPoint.y); personPointer = &Person; personPointer.name = "Mies"; say(Person.name); say(personPointer.name); Repeat frame; Until(key(_esc)) End Function int setXY(_point* p) Begin p.x = 3; // this is actually (*p).x = 3, but . can be used like this p.y = 5; // this is actually (*p).y = 5, but . can be used like this return 0; End
Used in example: say(), key(), Type, Global, Private, point
The & (offset) operator, when used with pointers, returns a void pointer to a variable. In the example it returns an int pointer to the variable my_int. The * (pointer) operator, when used with pointers, makes it so the pointer variable is not accessed, but the variable it's pointing to. In the example it changes access from my_int_pointer to my_int.