指標
宣告指標時請使用下列程序。
[storage-class-specifiers] [cv-qualifiers] type-specifiers
[ms-modifier] declarator ;
其中任何有效的指標宣告子可以用於declarator。 簡單的指標宣告的語法如下所示：
* [cv-qualifiers] identifier [= expression]
1. 宣告規範中：
選擇性儲存類別規範。 如需詳細資訊，請參閱規範。
選擇性const或volatile關鍵字將套用於指向物件的型別。
型別規範： 指向代表類型的物件型別的名稱。
2. 宣告子:
選擇性 Microsoft 特定輔助。 如需詳細資訊，請參閱 Microsoft 專屬的修飾詞。
* 運算子。
選擇性const或volatile將套用至指標本身的關鍵字。
識別項。
選擇性的初始設定式。
函式指標的宣告看起來像這樣：
(* [cv-qualifiers] identifier )( argument-list ) [cv-qualifers]
[exception specification] [= expression];
- 指標陣列，語法看起來像這樣：
* identifier [ [ constant-expression ] ]
不過，指標宣告子可以是更複雜。 如需詳細資訊，請參閱多個宣告。
多個宣告子以及其初始設定式可能會同時出現在後面的宣告規範的逗號分隔清單中的單一宣告。
指標宣告一個簡單的範例是：
char *pch;
上述的宣告指定的pch型別的物件會指向char。
是一個更複雜的範例
static unsigned int * const ptr;
上述的宣告指定的ptr是指標型別的物件，常數unsignedint靜態分割工期的任務。
下一個範例顯示如何在多個指標被宣告並初始化：
static int *p = &i, *q = &j;
在上述範例中，指標 p 和 q 指向物件型別的int ，並分別被初始化為 i 和 j 的地址。 儲存類別規範static會套用到這兩個指標。
範例
// pointer.cpp
// compile with: /EHsc
#include <iostream>
int main() {
int i = 1, j = 2; // local variables on the stack
int *p;
// a pointer may be assigned to "point to" the value of
// another variable using the & (address of) operator
p = & j;
// since j was on the stack, this address will be somewhere
// on the stack. Pointers are printed in hex format using
// %p and conventionally marked with 0x.
printf_s("0x%p\n", p);
// The * (indirection operator) can be read as "the value
// pointed to by".
// Since p is pointing to j, this should print "2"
printf_s("0x%p %d\n", p, *p);
// changing j will change the result of the indirection
// operator on p.
j = 7;
printf_s("0x%p %d\n", p, *p );
// The value of j can also be changed through the pointer
// by making an assignment to the dereferenced pointer
*p = 10;
printf_s("j is %d\n", j); // j is now 10
// allocate memory on the heap for an integer,
// initialize to 5
p = new int(5);
// print the pointer and the object pointed to
// the address will be somewhere on the heap
printf_s("0x%p %d\n", p, *p);
// free the memory pointed to by p
delete p;
// At this point, dereferencing p with *p would trigger
// a runtime access violation.
// Pointer arithmetic may be done with an array declared
// on the stack or allocated on the heap with new.
// The increment operator takes into account the size
// of the objects pointed to.
p = new int[5];
for (i = 0; i < 5; i++, p++) {
*p = i * 10;
printf_s("0x%p %d\n", p, *p);
}
// A common expression seen is dereferencing in combination
// with increment or decrement operators, as shown here.
// The indirection operator * takes precedence over the
// increment operator ++.
// These are particularly useful in manipulating char arrays.
char s1[4] = "cat";
char s2[4] = "dog";
char* p1 = s1;
char* p2 = s2;
// the following is a string copy operation
while (*p1++ = *p2++);
// s2 was copied into s1, so now they are both equal to "dog"
printf_s("%s %s", s1, s2);
}
另一個範例將說明使用指標在資料結構。 在這種情況下，連結清單。
// pointer_linkedlist.cpp
// compile with: /EHsc
#include <iostream>
using namespace std;
struct NewNode {
NewNode() : node(0){}
int i;
NewNode * node;
};
void WalkList(NewNode * ptr) {
if (ptr != 0) {
int i = 1;
while (ptr->node != 0 ) {
cout << "node " << i++ << " = " << ptr->i << endl;
ptr = ptr->node;
}
cout << "node " << i++ << " = " << ptr->i << endl;
}
}
void AddNode(NewNode ** ptr) {
NewNode * walker = 0;
NewNode * MyNewNode = new NewNode;
cout << "enter a number: " << endl;
cin >> MyNewNode->i;
if (*ptr == 0)
*ptr = MyNewNode;
else {
walker = *ptr;
while (walker->node != 0)
walker = walker->node;
walker->node = MyNewNode;
}
}
int main() {
char ans = ' ';
NewNode * ptr = 0;
do {
cout << "a (add node) d (display list) q (quit)" << endl;
cin >> ans;
switch (ans) {
case 'a':
AddNode(&ptr);
break;
case 'd':
WalkList(ptr);
break;
}
} while (ans != 'q');
}