C/C++ 的優先序

雖然到處都用括號括起來順序就一定不會錯，但是這樣寫code實在不方便閱讀
把優先序放在這邊方便參考

http://www.csee.umbc.edu/courses/104/fall06/burt/precedenceTable.html

Level	Symbol	Description	Associativity
1	++ -- ( ) [ ] -> .	Prefix increment Prefix decrement Function call and subexpression Array subscript Structure pointer Structure member	left to right
2	! ~ - + (type) * & sizeof	Logical negation 1's complement Unary negation Unary plus Type cast Pointer dereference Address of Size of	right to left
3	* / %	Multiplication Division Modulus (integer remainder)	left to right
4	+ -	Addition Subtraction	left to right
5	<< >>	Bitwise left shift Bitwise right shift	left to right
6	< <= > >=	Less than Less than or equal to Greater than Greater than or equal to	left to right
7	== !=	Equal test Not equal test	left to right
8	&	Bitwise AND	left to right
9	^	Bitwise exclusive OR (XOR)	left to right
10	|	Bitwise inclusive OR	left to right
11	&&	Logical AND	left to right
12	||	Logical inclusive OR	left to right
13	?:	Conditional test	right to left
14	= += -= *= /= %= <<= >>= &= ^= |	Assignment Compound add Compound subtract Compound multiply Compound divide Compound modulus Compound bitwise left shift Compound bitwise right shift Compound bise AND Compound bitwise exclusive OR Compound bitwise inclusive OR	right to left
15	, ++ --	Sequence point (list separator) Postfix increment Postfix decrement	left to right

C 函數指標的用法

C++有class, 那 C 呢??
以下介紹兩種方式，

方法一是定義的結構裡有函數pointer，然後再將結構宣告成陣列形式，好處是多定義了資料欄位

方法二是直接用陣列紀錄函式的pointer

//
// Method 1
//

+  int func1(int x)
+  {
+      return (2*x);
+  }
+  
+  int func2(int x) 
+  {
+      return (4*x);
+  }
+  
+  typedef struct 
+  {
+          int prio;
+          int ( *funcType )(int); //Function pointer
+  } TEST;
+  
+  int main()
+  {
+      
+      TEST MyTask[] =  {
+           { 1 , func1 },
+           { 2 , func2 }
+      };
+      
+      printf("x=2\n");
+  
+      printf("function priority = %d, output 2x= %d\n", MyTask[0].prio, MyTask[0].funcType(2) );
+  
+      printf("function priority = %d, output 4x= %d\n", MyTask[1].prio, MyTask[1].funcType(2) );
+      return 0;

+  }

--------------------------------Result----------------------------------

  x=2
  function priority = 1, output 2x=4
  function priority = 2, output 2x=8


//
//  Method 2
//

+  
+     void  Plus() {
+         printf("Plus\n");
+     }
+
+     void  Sub() {
+         printf("Sub\n");
+     }
+  
+     void main()
+     {
+         void ( *FuncGroup[] ) (void) = {Plus, Sub}; // 函數指標陣列
+
+         FuncGroup[ 0 ] (); // 呼叫函數
+         FuncGroup[ 1 ] ();
+     }

-----------------------------Result--------------------------------
  Plus
  Sub

C 結構位域用法

常看到一個位址中的記憶體內有不同的位元，他代表不同的旗標及暫存器，最常見的手法就是使用"結構"的"位域"。

+   typedef unsigned char BYTE;
+   
+   typedef union
+   {
+       BYTE all;
+       struct 
+       {
+           BYTE al:4;   // 將 al 設定為8bit
+           BYTE ah:4;  // 將 ah 設定為8bit
+       }part;  
+   }REGISTER8;
+   
+   REGISTER8 ax;
+   ax.all=0xCA;
+   printf("AH=%X, AL=%X\n",ax.part.ah, ax.part.al);
+
　　
從原本變數的最小單位short int(2bytes)，拆成上下兩個8bits的變數，這樣就符合PC裡AX暫存器分為上8bits(AH)及下8bits(AL)兩個暫存器了

#1 (2011-07-17) Blog was born !