# glxhyt

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入职一年了，这一年自己学到许多，但是忘记也很多，于是决定定下心来整理以前学到的，并且继续学习

二维数组和二级指针，这真是头疼的问题，困扰了我好几次，

先转一下wanpengcoder的二维数组和二级指针

Fun (int **p){}这里面的int **p //这里的p不是二维数组的指针，而是指向指针的指针，即二级指针。

int **p=(int**)a;//强制将二维数组指针转为指向指针的指针

p[0][1]=*(*(p+0)+1)；

a是指向整个数组的首地址,并不是int **;所以不要指望向函数fun里面传实参 p=a;

#include <iostream>

void fun(char ** p)

{

char (*p1)[10] = (char(*)[10])p;

std::cout<<p1[0][0]<<std::endl;

}

int main(int argc, char* argv[])

{

char data[][10] = {"abc","def"};

fun((char **)data);

return 0;

}

----------------------------------------------------------------华丽的分割线---------------------------------------------------------------------------------------------------------------------------

<c程序设计语言>中的关于这个的解释：

Newcomers to C are sometimes confused about the difference between a two-dimensional array and an array of pointers, such as name in the example above. Given the definitions

int a[10][20];

int *b[10];

then a[3][4] and b[3][4] are both syntactically legal references to a single int. But a is a true two-dimensional array: 200 int-sized locations have been set aside, and the conventional rectangular subscript calculation 20 * row +col is used to find the element a[row,col]. For b, however, the definition only allocates 10 pointers and does not initialize them; initialization must be done explicitly, either statically or with code. Assuming that each element of b does point to a twenty-element array, then there will be 200 ints set aside, plus ten cells for the pointers. The important advantage of the pointer array is that the rows of the array may be of different lengths. That is, each element of b need not point to a twenty-element vector; some may point to two elements, some to fifty, and some to none at all.

Although we have phrased this discussion in terms of integers, by far the most frequent use of arrays of pointers is to store character strings of diverse lengths, as in the function month_name. Compare the declaration and picture for an array of pointers:

char *name[] = { "Illegal month", "Jan", "Feb", "Mar" };￼

with those for a two-dimensional array:

char aname[][15] = { "Illegal month", "Jan", "Feb", "Mar" };

//我的理解是，当是指针数组的时候，可以直接传，如果是普通的二维数组的话应该就进行上面的转换。

一下是自己遇到问题：

问题1：

1#include "stdafx.h"
2
3#include <iostream>
4using namespace std;
5
6
7typedef struct tagNode_st
8{
9 char m_acData[10];
10 int m_iNo;
11}
Node_st;
12
13Node_st Root;
14
15int Fun(Node_st ** pst)
16{
17//Error
18#if 0
19 Node_st astNodeA[2= {{"xiaowang"1}{"xiaoming"2}};
20#else
21 static Node_st astNodeA[2= {{"xiaowang1"1}{"xiaoming1"1}}
22#endif
23 //static Node_st astNodeB[2] = {{"xiaowang2", 2}, {"xiaoming2", 2}};
24//static Node_st astNodeC[2] = {{"xiaowang3", 3}, {"xiaoming3", 3}};
25*pst = astNodeA;
26
27 return 0;
28}

29
30int _tmain(int argc, _TCHAR* argv[])
31{
32 Node_st st[2][2];
33
34 //TypeA
35 Fun((Node_st**)st);
36   //1.error
37 cout<<st[0][0].m_acData<<endl;
38 cout<<st[0][0].m_iNo<<endl<<endl;
39
40 //2.error
41 cout<<(*st)->m_acData<<endl;
42 cout<<(*st)->m_iNo<<endl<<endl;
43
44 //3.right
45 cout<<(*(Node_st**)st)->m_acData<<endl;
46 cout<<(*(Node_st**)st)->m_iNo<<endl<<endl;
47
48 //Typde B
49 Node_st *pstTemp[2= {&st[0][0], &st[1][0]};
50 Fun(&pstTemp[0]);
51 //Right
52 cout<<(pstTemp[0])->m_acData<<endl;
53 cout<<(pstTemp[0])->m_iNo<<endl<<endl;
54
55 //Error
56 cout<<(st[0][0]).m_acData<<endl;
57 cout<<(st[0][0]).m_iNo<<endl<<endl;
58
59 //Right
60 cout<<(*(Node_st**)st)->m_acData<<endl;
61 cout<<(*(Node_st**)st)->m_iNo<<endl<<endl;
62
63 //Typde C
64
65 Node_st *pstTemp2[2= {NULL, NULL};
66 Fun(&pstTemp2[0]);
67 //Right
68 cout<<(pstTemp2[0])->m_acData<<endl;
69 cout<<(pstTemp2[0])->m_iNo<<endl<<endl;
70
71 return 0;
72}

73

1 int iaArray[2][2= {1124};
2
3 int **= (int**)iaArray;
4
5 for (int i = 0; i < 4++ i)
6 {
7  cout<<"i:"<<i<<" "<<q[i]<<endl;
8 }

9

和：
1 int iaArrayTemp[5] = {1, 2, 3, 4, 5};
2 int **p = (int**)&iaArrayTemp;
3 p++;
4 cout<<*p<<endl;

1#include <iostream>
2using namespace std;
3
4int main()
5{
6 int iaArray[5] = {1, 2, 3, 4, 5};
7
8#if 0
9
10 int *p = (int*)(&iaArray+1)-1;
11 cout<<*p<<endl;
12
13 int *q = (int*)(&iaArray+1);
14 cout<<*(q-1)<<endl;
15
16 int **qq = (int**)(&iaArray+1);
17 cout<<*(qq-1)<<endl;
18
19#else
20 int iaAry[2][2] = {1, 2, 3, 4};
21
22 int *p = (int*)(&iaAry+1)-1;
23 cout<<*p<<endl;
24
25 int *q = (int*)(&iaAry+1);
26 cout<<*(q-1)<<endl;
27
28 int **qq = (int**)(&iaAry+1);
29 cout<<*(qq-1)<<endl;
30#endif
31 return 0;
32}

3：注意函数传递，指针，引用

在指针引用&*，**的时候是改变的指针，这个一般主要是里面涉及到内存分配，
或者获取的是静态区域，或者是全局的区域，传递的时候一般都是传，空指针。

传递*，&，是改变的数组的值。一般都是传递的是非空的，一般要再函数中增加
assert(NULL != p);

4.const ，Enum，static const ...待续

快0:00，笑一笑，睡觉了
posted on 2011-11-21 23:55 郭龙 阅读(5473) 评论(0)  编辑 收藏 引用