Changes between Version 5 and Version 6 of ResumedC

Timestamp:

Apr 28, 2009, 5:18:34 PM (16 years ago)

Author:

Thanatermesis

Comment:

--

ResumedC

@@ -93 +93 @@
 
 
-
 === Variables ===
 
@@ -106 +105 @@
 '''signed''': means ''with sign'', so, values negative and positive, for example if the '''char''' variable has a limit of 255 values, using the '''sign''' mode we can use from '''-128''' (negative) to '''127''' (positive), and using '''unsigned''' we can use from '''0''' to '''255'''
 
+
+
+
+=== Constants ===
+
 The '''constant''' variables are constants, so they can't change, by convention they are in upper-case
+
+{{{
+#!C
+/* The variable answer_p is a constant and can't change, but the pointer address can be changed. */
+const char *answer_p = "Forty-Two";
+
+/* If we want to have the inverse to this, we need to put the const AFTER the *, so: */
+char *const answer_p = "Forty-Two";
+   /* Now the pointer can't change the address value, but the data (Forty-Two) can be changed */
+
+/* Finally, we can set both in constant with something like: */
+const char *const answer_p = "Forty-Two";
+}}}
 
 
@@ -157 +174 @@
 
 
+
+
+
 === Structures ===
 
@@ -172 +192 @@
 
 /* Initialization of an array of structures: */
-struct time start_stop[2] = {
-  { 10, 0 },
-  { 12, 0 }
-};
-}}}
-
+struct time start_stop[2] = 
+   {
+      { 10, 0 },
+      { 12, 0 }
+   };
+}}}
 
 ==== Packaged structures ====
@@ -196 +216 @@
 
 
+
+
 === Pointers ===
 
-With pointers you can modify directly the data of a variable (see #functions)
+With pointers you can modify directly the data of a variable (see the '''functions''' section)
+
+You can access to a lot more fast way to structure elements and other big pieces that are inside big ones, so you can optimize your code with the correct usage of pointers, 
+
+If you want to have a pointer to an array, you need to point to the first array of the variable, so:
+{{{
+#!C
+/* array of 5 elements */
+char arr[5];
+
+/* pointer 'arr_p' to the array 'arr'
+char *arr_p = &arr[0];
+
+*(array_p + 1) /* Equivalent */
+(*array_p + 1 ) /* Not Equivalent */
+}}}
+
 
 
@@ -254 +292 @@
 
 
+=== Optimizations ===
+
+An array do increments of the array level in order to search/find something, by using pointers is a lot faster than generate an index operation, for example:
+{{{
+#!C
+while ((*array_p) != 0)
+   ++array__p;
+}}}
+
+Imagine a structure of 226 bytes long, for example, that's a lot of data to move around, so you can declare an array of pointers:
+{{{
+#!C
+struct mailing {
+   ...
+} list[MAX_ENTRIES];
+
+struct mailing *list_p[MAX_ENTRIES];
+
+for (current...
+   list_p[current] = &list[current];
+}}}
+ Now you have to move only 4-byte around, instead of 226 all the time
+
+
+
+
+
+
+
 
 
@@ -261 +328 @@
 
 If you want to pass something defined (to use with #ifdef, for example) in the moment of the compilation, you will add options to the compiler (gcc) like -DDEBUG or -DMAX=10
+
+
+
+