指標
指標是使用下列序列宣告。
[storage-class-specifiers] [cv-qualifiers] type-specifiers
[ms-modifier] declarator ;
其中可能會使用 declarator 的任何有效的指標宣告子。簡單指標宣告子的語法如下：
* [cv-qualifiers] identifier [= expression]
1. 宣告指定名稱：
選擇性的儲存類別規範。 如需詳細資訊，請參閱指定名稱。
選擇性套用至將指向之物件類型的 const 或 volatile 關鍵字。
類型指定名稱：表示將指向之物件類型的類型名稱。
2. 宣告子：
選擇性的 Microsoft 專有修飾詞。 如需詳細資訊，請參閱 Microsoft 專有的修飾詞。
* 運算子。
選擇性套用至指標本身的 const 或 volatile 關鍵字。
識別碼。
選擇性的初始設定式。
函式指標的宣告子如下所示：
(* [cv-qualifiers] identifier )( argument-list ) [cv-qualifers]
[exception specification] [= expression];
- 對於指標陣列，其語法如下所示：
* identifier [ [ constant-expression ] ]
不過，指標宣告子更為複雜。 如需詳細資訊，請參閱宣告子。
多個宣告子及其初始設定式可以一起出現在逗號分隔清單的單一宣告中，其後為宣告指定名稱。
指標宣告的簡單範例如下：
char *pch;
上述宣告中將 pch 指定為指向類型為 char 的物件。
較複雜的範例為：
static unsigned int * const ptr;
上述宣告將 ptr 指定為常數指標，以指向具有靜態儲存期的 unsigned int 類型物件。
下列範例顯示如何宣告及初始化多個指標：
static int *p = &i, *q = &j;
上述範例中，指標 p 和 q 皆指向類型為 int 的物件，並分別初始化為 i 和 j 的位址。兩個指標皆會套用儲存類別指定名稱 static。
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);
}
另一個範例示範如何在資料結構中使用指標，此例中為連結清單。
// 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');
}