高素质编程师湖南大学语言课件第八章.ppt

第八章 指针 C程序设计中使用指针可以: l使程序简洁、紧凑、高效 l有效地表示复杂的数据结构 l动态分配内存 l得到多于一个的函数返回值 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 8.1 指针的概念 变量与地址 程序中: int i; float k; 内存中每个字节有一个编号-地址 . 2000 2001 2002 2005 内存 0 2003 i k 编译或函数调用时为其分配内存单元 变量是对程序中数据 存储空间的抽象 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. . 2000 2004 2006 2005 整型变量i 10 变量i_pointer 2001 2002 2003 指针与指针变量 v指针：一个变量的地址 v指针变量：专门存放变量地址的变量叫 2000 指针 指针变量 变量的内容 变量的地址 指针变量 变量 变量地址(指针) 变量值 指向 地址存入 指针变量 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. -直接访问 指针变量 . 2000 2004 2006 2005 整型变量i 10 变量i_pointer 2001 2002 2003 2000 3 例 *i_pointer=20; -间接访问 20Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 指针变量 . 2000 2004 2006 2005 整型变量i 10 变量i_pointer 2001 2002 2003 2000 整型变量k 例 k=i; -直接访问 k=*i_pointer; -间接访问 10 例 k=i; k=*i_pointer; Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 8.2 指针变量 指针变量与其所指向的变量之间的关系 指针变量的定义 v一般形式： 存储类型 数据类型 *指针名； 3 变量i 2000 i_pointer *i_pointer i*i_pointer *i_pointer=3 3 变量i 2000 i_pointer *i_pointer i*i_pointer *i_pointer=3 合法标识符 指针变量本身的存储类型指针的目标变量的数据类型 表示定义指针变量 不是*运算符 例 int *p1,*p2; float *q ; static char *name; 注意： 1、int *p1, *p2; 与 int *p1, p2; 2、指针变量名是p1,p2 ,不是*p1,*p2 3、指针变量只能指向定义时所规定类型的变量 4、指针变量定义后，变量值不确定，应用前必须先赋值 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 指针变量的初始化 一般形式：存储类型 数据类型 *指针名=初始地址值； 赋给指针变量， 不是赋给目标变量 例 int i; int *p= 变量必须已说明过 类型应一致 例 int *p= int i; 例 int i; int *p= int *q=p; 用已初始化指针变量作初值 例 main( ) int i; static int *p= () 不能用auto变量的地址 去初始化static型指针 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 例 main( ) int i=10; int *p; *p=i; printf(“%d”,*p); 危险！ 例 main( ) int i=10,k; int *p; p= *p=i; printf(“%d”,*p); 指针变量必须先赋值,再使用 . 2000 2004 2006 2005 整型变量i 10 指针变量p 2001 2002 2003 随机 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 零指针与空类型指针 v零指针：(空指针) l定义:指针变量值为零 l表示： int * p=0; p指向地址为0的单元， 系统保证该单元不作它用 表示指针变量值没有意义 #define NULL 0 int *p=NULL: lp=NULL与未对p赋值不同 l用途: u避免指针变量的非法引用 u在程序中常作为状态比较 例 int *p; while(p!=NULL) . vvoid *类型指针 l表示: void *p; l使用时要进行强制类型转换 例 char *p1; void *p2; p1=(char *)p2; p2=(void *)p1; 表示不指定p是指向哪一种 类型数据的指针变量 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 例 指针的概念 main() int a; int *pa= a=10; printf(“a:%dn“,a); printf(“*pa:%dn“,*pa); printf(“ printf(“pa:%x(hex)n“,pa); printf(“ 运行结果： a:10 *pa:10 scanf(“%d,%d“, p1= p2= if(ap2 表示p1指的元素在后 up1=p2 表示p1与p2指向同一元素 l若p1与p2不指向同一数组，比较无意义 lp=NULL或p!=NULL Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 数组元素表示方法 a0 a1 a2 a3 a9 . a a+9 a+1 a+2 地址 元素 下标法 a0 a1 a2 a9 a0 a1 a2 a3 a9 . p p+9 p+1 p+2 地址 元素 指针法 *p *(p+1) *(p+2) *(p+9) 变址运算符 ai *(a+i) ai pi *(p+i) *(a+i) *a *(a+1) *(a+2) *(a+9) p0 p1 p2 p9 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. a0 a1 a2 a3 a4 例 数组元素的引用方法 main() int a5,*pa,i; for(i=0;iy) z=x; else z=y; return(z); main() int max(int ,int), (*p)(); int a,b,c; p=max; scanf(“%d,%d“, c=(*p)(a,b); printf(“a=%d,b=%d,max=%dn“,a,b,c); int max(int x,int y) int z; if(xy) z=x; else z=y; return(z); Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 用函数指针变量作函数参数 例 用函数指针变量作参数，求最大值、最小值和两数之和 void main() int a,b,max(int,int), min(int,int),add(int,int); void process(int,int,int (*fun)(); scanf(“%d,%d“, process(a,b,max); process(a,b,min); process(a,b,add); void process(int x,int y,int (*fun)() int result; result=(*fun)(x,y); printf(“%dn“,result); max(int x,int y) printf(“max=”);printf(“max=”); return(xy?x:y); return(xy?x:y); min(int x,int y) printf(“min=”);printf(“min=”); return(x*y) return x; else return y; main() int a=2,b=3; int *p; p=f1( printf(“%dn“,*p); . 2000 2008 200A 2002 2004 2006 2 3 指针变量y 指针变量x (f1) 2002 2000 COPY 变量a 变量b (main) 指针变量p *Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 例 写一个函数，求两个int型变量中居于较大值的变量的地址 . 2000 2008 200A 2002 2004 2006 2 变量a 变量b (main) 3 指针变量p * 2002 int *f3(int *x,int *y) if(*x*y) return x; else return y; main() int a=2,b=3; int *p; p=f1( printf(“%dn“,*p); Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 例 写一个函数，求两个int型变量中居于较大值的变量的地址 int *f3(int x,int y) if(xy) return else return main() int a=2,b=3; int *p; p=f3(a, b); printf(“%dn“,*p); . 2000 2008 200A 2002 2004 2006 2 3 变量y 变量x (f3) 3 2 COPY 变量a 变量b (main) 指针变量p *Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 例 写一个函数，求两个int型变量中居于较大值的变量的地址 不能返回形参或局部变量 的地址作函数返回值 . 2000 2008 200A 2002 2004 2006 2 变量a 变量b (main) 3 指针变量p * 200A int *f3(int x,int y) if(xy) return else return main() int a=2,b=3; int *p; p=f3(a,b); printf(“%dn“,*p); Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 8.7 指针数组和多级指针 用于处理二维数组或多个字符串 指针数组 v定义：数组中的元素为指针变量 v定义形式：存储类型 数据类型 *数组名数组长度说明 ； 例 int *p4; 指针所指向变量的数据类型指针本身的存储类型 区分int *p4与int (*p)4 v指针数组赋值与初始化 赋值: main() int b23,*pb2; pb0=b0; pb1=b1; int *pb2 pb0 pb1 int b23 1 2 3 2 4 6 初始化: main() int b23,*pb =b0,b1; int *pb2 pb0 pb1 int b23 1 2 3 2 4 6 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. v指针数组赋值与初始化 L i s p 0 F o r t r a n 0 B a s i c 0 p0 p1 p2 p30 赋值: main() char a=“Fortran“; char b=“Lisp“; char c=“Basic“; char *p4; p0=a; p1=b; p2=c; p3=NULL; 或: main() char *p4; p0= “Fortran“; p1= “Lisp“; p2= “Basic“; p3=NULL; 初始化: main() char *p=“Fortran“, “Lisp“, “Basic“,NULL; L i s p 0 F o r t r a n 0 B a s i c 0 p0 p1 p2 p30 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. char name59=“gain”,“much”,“stronger”, “point”,“bye”; char *name5=“gain”,“much”,“stronger”, “point”,“bye”; g a i n 0 s t r o n g e r 0 p o i n t 0 m u c h 0 name0 name1 name2 name3 name4 b y e 0 g a i n 0 s t r o n g e r 0 p o i n t 0 m u c h 0 b y e 0 v二维数组与指针数组区别： 二维数组存储空间固定 字符指针数组相当于可变列长的二维数组 分配内存单元=数组维数*2+各字符串长度 指针数组元素的作用相当于二维数组的行名 但指针数组中元素是指针变量 二维数组的行名是地址常量 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. main() int b23,*pb2; int i,j; for(i=0;i0) k=j; if(k!=i) temp=namei; namei=namek; namek=temp; name0 name1 name2 name3 name4 name Great Wall FORTRAN Computer Follow me BASIC k jk j j j i=0 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 例 对字符串排序（简单选择排序） main() void sort(char *name,int n), print(char *name,int n); char *name=“Follow me“,“BASIC“, “Great Wall“,“FORTRAN“,“Computer “; int n=5; sort(name,n); print(name,n); void sort(char *name,int n) char *temp; int i,j,k; for(i=0;i0) k=j; if(k!=i) temp=namei; namei=namek; namek=temp; name0 name1 name2 name3 name4 name Great Wall FORTRAN Computer Follow me BASIC k k j j j i=1 k Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 例 对字符串排序（简单选择排序） main() void sort(char *name,int n), print(char *name,int n); char *name=“Follow me“,“BASIC“, “Great Wall“,“FORTRAN“,“Computer “; int n=5; sort(name,n); print(name,n); void sort(char *name,int n) char *temp; int i,j,k; for(i=0;i0) k=j; if(k!=i) temp=namei; namei=namek; namek=temp; name0 name1 name2 name3 name4 name Great Wall FORTRAN Computer Follow me BASIC k kj j i=2 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 例 对字符串排序（简单选择排序） main() void sort(char *name,int n), print(char *name,int n); char *name=“Follow me“,“BASIC“, “Great Wall“,“FORTRAN“,“Computer “; int n=5; sort(name,n); print(name,n); void sort(char *name,int n) char *temp; int i,j,k; for(i=0;i0) k=j; if(k!=i) temp=namei; namei=namek; namek=temp; name0 name1 name2 name3 name4 name Great Wall FORTRAN Computer Follow me BASIC k k j i=3 Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. 例 对字符串排序（简单选择排序） main() void sort(char *name,int n), print(char *name,int n); char *name=“Follow me“,“BASIC“, “Great Wall“,“FORTRAN“,“Computer “; int n=5; sort(name,n); print(name,n); void sort(char *name,int n) char *temp; int i,j,k; for(i=0;i0) k=j; if(k!=i) temp=namei; namei=namek; namek=temp; name0 name1 name2 name3 name4 name Great Wall FORTRAN Computer Follow me BASIC Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile .Created with Aspose.Slides for .NET 3.5 Client Profile . Copyright 2004-2011 Aspose Pty Ltd.Copyright 2004-2011 Aspose Pty Ltd. Evaluation only.Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile