数组与字符串、字符指针与其他类型指针、赋值参数、指针参数以及引用参数、函数指针

本文深入探讨了 C++ 中数组与字符串的区别、字符指针与其他类型指针的不同用法、参数传递机制（包括按值、按指针和按引用），以及函数指针的应用实例。

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原文地址：http://www.cppblog.com/xingjiegaojue/archive/2009/08/12/93099.aspx

数组与字符串、字符指针与其他类型指针、赋值参数、指针参数以及引用参数、函数指针

◆数组和字符串
从表面上看，一个字符串就是一个字符数组，但在C++语句中，两者并不完全相同。
字符串是一个以串尾符"\0"结尾的字符型数组，但任一个字符型数组不见得必为字符串(因为其中可以不包含"\0"结尾字符)。

char string1[ 7 ] = " China " ;

char string2[] = " China " ;

char string3[ 7 ] = {'C','h','i','n','a'} ;

char string4[ 7 ] = {'C','h','i','n','a','\0'} ;

string1的长度为7，赋初值后其前6个元素已被赋值(第6个元素为'\0')；
string2的长度为6(第6个元素为'\0')；
string3的长度为7，最后没有串尾符'\0'；
string4的长度为7，赋初值后与string1相同。

◆字符指针与其他类型指针的使用区别
读下列程序：

#include < iostream >
2

using namespace std;
3

int main()
4

{
5

char str[10]="abcdefghi";
6

int a[10]={0,1,2,3,4,5,6,7,8,9};
7

cout<<"'cout<<str'=>"<<str<<endl;
8

cout<<"'cout<<a'=>"<<a<<endl;
9

cout<<"--------------------"<<endl;
10

cout<<"'cout<<&str'=>"<<&str<<endl;
11

cout<<"'cout<<&a'=>"<<&a<<endl;
12

cout<<"--------------------"<<endl;
13

cout<<"'cout<<(int*)str'=>"<<(int*)str<<endl;
14

cout<<"'cout<<(double*)a'=>"<<(double*)a<<endl;
15

cout<<"--------------------"<<endl;
16

cout<<"'cout<<str+1'=>"<<str+1<<endl;
17

cout<<"'cout<<a+1'=>"<<a+1<<endl;
18

cout<<"--------------------"<<endl;
19

cout<<"'cout<<&str[1]'=>"<<&str[1]<<endl;
20

cout<<"'cout<<&a[1]'=>"<<&a[1]<<endl;
21

cout<<"--------------------"<<endl;
22

cout<<"'cout<<(int*)(str+1)'=>"<<(int*)(str+1)<<endl;
23

cout<<"'cout<<(double*)(a+1)'=>"<<(double*)(a+1)<<endl;
24

cout<<"--------------------"<<endl;
25

cout<<"'cout<<(double*)(&str[1])'=>"<<(double*)(&str[1])<<endl;
26

cout<<"'cout<<(double*)(&a[1])'=>"<<(double*)(&a[1])<<endl;
27

cout<<"--------------------"<<endl;
28

return 0;
29

}
30

输出结果：

' cout<<str ' => abcdefghi
2

' cout<<a ' => 0X0065FDC4 // 存放地址，可以不同(下同)
3

--------------------------
4

' cout<<&str ' => 0X0065FDEC
5

' cout<<&a ' => 0X0065FDC4
6

--------------------------
7

' cout<<(int*)str ' => 0X0065FDEC
8

' cout<<(double*)a ' => 0X0065FDC4
9

--------------------------
10

' cout<<str+1 ' => bcdefghi
11

' cout<<a+1 ' => 0X0065FDC8
12

--------------------------
13

' cout<<&str[1] ' => bcdefghi
14

' cout<<&a[1] ' => 0X0065FDC8
15

--------------------------
16

' cout<<(int*)(str+1) ' => 0X0065FDED
17

' cout<<(double*)(a+1) ' => 0X0065FDC8
18

--------------------------
19

' cout<<(double*)(&str[1]) ' => 0X0065FDED
20

' cout<<(double*)(&a[1]) ' => 0X0065FDC8
21

--------------------------

分析：
字符指针与其他类型的指针(如int型指针)在使用上是有所区别的(字符指针具有其特殊性)。如，输出字符数组名即字符指针
，就是输出字符指针所指向的那一个字符串；而输出int型数组名即int型指针，就是输出当前的指针值(一个地址)。但输出
字符数组名取地址，或输出int型数组名取地址，都可以输出当前的指针值(一个地址)。另外，若将字符数组名即字符指针
的类型进行转换后，输出的将是当前的指针值(一个地址)。

◆赋值参数、指针参数以及引用参数的使用区别
读下面程序：

#include < iostream >
2

using namespace std;
3

int myFunc( int i1, int * pi21, int *& pi22, int & ri3, char * str);
4

int main()
6

{
7

int i=1,a[2]={21,202},*pa=a,b[2]={21,202},*pb=b,r=3456;
8

char s[]="ABCDEFG";
9

cout<<"--------In main position 1--------"<<endl;
10

cout<<"i,*pa,*pb,r,s="<<i<<","<<*pa<<","<<*pb<<","
11

<<r<<","<<s<<endl;
12

cout<<"a[0],a[1],b[0],b[1]="<<a[0]<<","<<a[1]<<","
13

<<b[0]<<","<<b[1]<<endl;
14

int tmp=myFunc(i,pa,pb,r,s);
15

cout<<"--------In main position2 2--------"<<endl;
16

cout<<"i,*pa,*pb,r,s="<<i<<","<<*pa<<","<<*pb<<","
17

<<r<<","<<s<<endl;
18

cout<<"a[0],a[1],b[0],b[1]="<<a[0]<<","<<a[1]<<","
19

<<b[0]<<","<<b[1]<<endl;
20

cout<<"tmp="<<tmp<<endl;
21

return 0;
22

}
23

int myFunc( int i1, int * pi21, int *& pi22, int & ri3, char * str)
24

{
25

cout<<"--------In myFunc position 1-------"<<endl;
26

cout<<"i1,*pi21,*pi22,ri3,str="<<i1<<","<<*pi21<<","
27

<<*pi22<<","<<ri3<<","<<str<<endl;
28

i1++;
29

pi21++;
30

pi22++;
31

ri3++;
32

(*str)++;
33

cout<<"--------In myFunc position 2-------"<<endl;
34

cout<<"i1,*pi21,*pi22,ri3,str="<<i1<<","<<*pi21<<","
35

<<*pi22<<","<<ri3<<","<<str<<endl;
36

i1++;
37

(*pi21)++;
38

(*pi22)++;
39

ri3++;
40

str++;
41

cout<<"--------In myFunc position 3-------"<<endl;
42

cout<<"i1,*pi21,*pi22,ri3,str="<<i1<<","<<*pi21<<","
43

<<*pi22<<","<<ri3<<","<<str<<endl;
44

return i1;
46

}
47

运行结果为：

-------- In main position 1 --------

i, * pa, * pb,r,s = 1 , 21 , 21 , 3456 ,ABCDEFG

a[ 0 ],a[ 1 ],b[ 0 ],b[ 1 ] = 21 , 202 , 21 , 202

-------- In myFunc position 1 -------

i1, * pi21, * pi22,ri3,str = 1 , 21 , 21 , 3456 ,ABCDEFG

-------- In myFunc position 2 -------

i1, * pi21, * pi22,ri3,str = 2 , 202 , 202 , 3457 ,BBCDEFG

-------- In myFunc position 3 -------

i1, * pi21, * pi22,ri3,str = 3 , 203 , 203 , 3458 ,BCDEFG

-------- In main position2 2 --------

i, * pa, * pb,r,s = 1 , 21 , 203 , 3458 ,BBCDEFG

a[ 0 ],a[ 1 ],b[ 0 ],b[ 1 ] = 21 , 203 , 21 , 203

tmp = 3

◆函数指针
读程序：

#include < iostream >
2

#include < cmath >
3

using namespace std;
4

double func1( double x);
5

double func2( double y);
6

double func3( double z);
7

void processing( double x, double ( * fpt)( double ));
8

int main()
10

{
11

double x,res;
12

double (*fp)(double);
13

cout<<"Input a real number:";
14

cin>>x;
15

fp=func1;
16

res=(*fp)(x);
17

cout<<"res=(*fp)(x)="<<res<<endl;
18

fp=func2;
19

res=(*fp)(x);
20

cout<<"res=(*fp)(x)="<<res<<endl;
21

processing(x,func3);
22

fp=func3;
23

processing(x,fp);
24

return 0;
25

}
26

double func1( double x)
27

{
28

cout<<" ---Call func1: 1/x="<<1/x<<endl;
29

return (1/x);
30

}
31

double func2( double x)
32

{
33

cout<<" ---Call func2: x*x="<<x*x<<endl;
34

return (x*x);
35

}
36

double func3( double x)
37

{
38

cout<<" ---Call func3: sqrt(x)="<<sqrt(x)<<endl;
39

return sqrt(x);
40

}
41

void processing( double x, double ( * fpt)( double ))
42

{
43

cout<<" ---Call processing"<<endl;
44

double result=(*fpt)(x);
45

cout<<" ---result=(*fpt)(x)="<<result<<endl;
46

}
47

结果显示：

Input a real number: 5.5

--- Call func1: 1 / x = 0.181818

res = ( * fp)(x) = 0.181818

--- Call func2: x * x = 30.25

res = ( * fp)(x) = 30.25

--- Call processing

--- Call func3: sqrt(x) = 2.34512

--- result = ( * fpt)(x) = 2.34512

--- Call processing

--- Call func3: sqrt(x) = 2.34512

--- result = ( * fpt)(x) = 2.34512