Introduction to pointers in C/C++

Introduction to pointersin C/C++

Pointers • 特殊變數 • 存放變數在記憶體中的位址 • MinGW C++中佔用 4 bytes • 間接定址取執法變數指標變數變數內容位址

Why pointers? • 函數回傳一個以上的值 • 傳遞陣列或字串參數 • 建構鏈結相關的資料結構，如linked list, etc. • 記憶體配置函數malloc()或fopen()等必須使用指標

Declaration • 型別 *變數名稱; • int *ptri; • char *ptrch; • float *ptrf=NULL;

Operations for pointers • &: 位址運算子 • *: 依值取值運算子 • E.G.: *(&ptri)  ptri • ++: 指標加法 (加上所指型別變數之長度) • --: 指標減法 (減去所指型別變數之長度) • E.G.:int *ptri;ptri++; /* 將ptri的值加4 */

Pointers and Arrays • Array variable is a pointer • E.G.:int a[3]={1,2,3};*aa[0]1*(a+1)a[1]2*(a+2)a[2]a&a[0]a+1&a[1]a+2&a[2]

Call by value, Call by pointer, and Call by reference (address) • int func(int, int)  call by value • int func(int*, int*)  call by pointer • Int func(int&, int&)  call by reference

Call by value • //檔名:swap1.cpp • #include <iostream.h> • void swap(int, int); • main() { • int i=3,j=8; • cout<<i<<j<<endl; • swap(i, j); • cout<<i<<j<<endl; • } • void swap(int a, int b) { • int temp=a; • a=b; • b=temp; • }

Call by pointer • //檔名:swap2.cpp • #include <iostream.h> • void swap(int *, int*); • main() { • int i=3,j=8; • cout<<i<<j<<endl; • swap(&i, &j); • cout<<i<<j<<endl; • } • void swap(int* a, int *b) { • int temp=*a; • *a=*b; • *b=temp; • }

Call by pointer • //檔名:swap3.cpp • #include <iostream.h> • void swap(int &, int&); • main() { • int i=3,j=8; • cout<<i<<j<<endl; • swap(i, j); • cout<<i<<j<<endl; • } • void swap(int& a, int &b) { • int temp=a; • a=b; • b=temp; • }

Pointer of pointer • int i=5, *a, **b; • a=&i; • b=&a; • What is the value of • *a • a • &a • **b • *b • b • &b

Q&A

Introduction to pointers in C/C++