自动变量和开辟内存的生存期和作用域探讨

 1 // CUITestingCPP.cpp : 定义控制台应用程序的入口点。
 2 //
 3 
 4 #include "stdafx.h"
 5 #include <iostream>
 6 using namespace std;
 7 
 8 typedef struct CvHistogra
 9 {
10     int type;
11     float** thresh2;
12     int aas;
13 }
14 CvHistogra;
15 
16 CvHistogra * createHist()
17 {
18     CvHistogra hist_value;
19     hist_value.type = 2;
20     cout << "hist_value变量地址：" << &hist_value << endl;
21     cout << "hist_value成员type的值：" << hist_value.type << endl;
22     return &hist_value;
23 }
24 
25 CvHistogra * mallocHist()
26 {
27     CvHistogra *  hist_value = (CvHistogra*)malloc(sizeof(CvHistogra));
28     hist_value->type = 5;
29     cout << "hist_value变量地址：" << hist_value << endl;
30     cout << "hist_value成员type的值：" << hist_value->type << endl;
31 
32     return hist_value;
33 }
34 
35 int _tmain(int argc, _TCHAR* argv[])
36 {
37     CvHistogra * histTest;
38     histTest = createHist();
39 
40     cout << "histTest成员type的值：" << histTest->type << endl;
41     cout << "histTest成员type的值再输出一次值改变：" << histTest->type << endl;
42     cout << "histTest  指针的值：" << histTest << endl;
43 
44     //free(histTest);//histTest所指向的内存不是malloc开辟的，是栈上的内存，所以使用free释放失败
45 
46     cout << endl;
47     cout << endl;
48 
49     CvHistogra * mallHist;
50     mallHist = mallocHist();
51     cout << "mallHist  指针的值：" << mallHist << endl;
52     cout << "mallHist 成员type的值：" << mallHist->type << endl;
53     cout << "mallHist 成员type的值：" << mallHist->type << endl;
54 
55     mallHist->aas=9;
56 
57     free(mallHist);
58     mallHist = NULL; //释放完毕要置为null，不然下边一行还能够输出，只是输出的是错误的值
59     //cout << "mallHist 成员type的值：" << mallHist->type << endl;
60 
61     system("pause");
62 
63     return 0;
64 }