码迷，mamicode.com
首页 > Windows程序 > 详细

WinCE 下结构体占用空间的分析

时间：2016-02-21 16:57:18      阅读：203      评论：0      收藏：0      [点我收藏+]

标签：

年前辞职了，准备年后找工作。
所以在网上查找一下 C/C++ 基础方面的面试题，个人感觉这方面还是要准备一下。
虽然后面的应聘没有用到所准备的这些，算是学习一下。
在学习过程中，注意到一些关于结构体占用内存空间大小(sizeof 与 padding byte)的问题，觉得挺有趣的。
在 WinCE 以前的小系统(嵌入式系统)编程时，特别注意内存的使用情况；但到了 WinCE 系统后，由于设备一般都有 128M(或更多)的内存，所以在内存的使用与优化上很多人已经不太注意。
嵌入式方面的程序员，还是有必要了解以下关于结构体占用空间这个问题。

  1 typedef struct TwoBytes_S  
  2 {  
  3     char cOne;  
  4     char cTwo;  
  5 }TwoBytesEml;  
  6   
  7   
  8 typedef struct FourBytes_S  
  9 {  
 10     char cOne;  
 11     char cTwo;  
 12     char cThree;  
 13     char cFour;  
 14 }FourBytesEml;  
 15   
 16   
 17 typedef struct EightBytes_S  
 18 {  
 19     char cOne;  
 20     char cTwo;  
 21     char cThree;  
 22     char cFour;  
 23     char cFive;  
 24     char cSix;  
 25     char cSeven;  
 26     char cEight;  
 27 }EightBytesEml;  
 28   
 29   
 30 // 结构体实际占用的空间大小与结构体中占用空间最大的成员有什么关系?  
 31 // 结论: 结构体的大小为结构体中占用字节最大的成员的倍数。   
 32   
 33   
 34 // 对比 TestOder, TestOrder3 和 TestOder2 占用内存空间的情况  
 35 typedef struct TestOrder_S  
 36 {  
 37     char cFirst;  
 38     char cSecond;  
 39     int iFirst;  
 40     char cThird;  
 41     char cFourth;  
 42 }TestOrder;  
 43   
 44   
 45 typedef struct TestOrder2_S  
 46 {  
 47     int iFirst;  
 48     char cFirst;  
 49     char cSecond;  
 50     char cThird;  
 51     char cFourth;  
 52 }TestOrder2;  
 53   
 54   
 55 typedef struct TestOrder3_S  
 56 {  
 57     int iFirst;  
 58     char cFirst;  
 59     char cSecond;  
 60     char cThird;  
 61 }TestOrder3;  
 62   
 63   
 64 // 对比 TestShort 和 TestShortEml 占用内存空间的情况  
 65 typedef struct TestShort_S  
 66 {  
 67     char cOne;  
 68     short sAlign;  
 69 }TestShort;  
 70 typedef struct TestShortEml_S  
 71 {  
 72     char cOne;  
 73     TwoBytesEml sAlign;  
 74 }TestShortEml;  
 75   
 76   
 77 // 对比 TestInt 和 TestIntEml 占用内存空间的情况  
 78 typedef struct TestInt_S  
 79 {  
 80     char cOne;  
 81     int iAlign;  
 82 }TestInt;  
 83 typedef struct TestIntEml_S  
 84 {  
 85     char cOne;  
 86     FourBytesEml iAlign;  
 87 }TestIntEml;  
 88   
 89   
 90 // 对比 TestDouble 和 TestDoubleEml 占用内存空间的情况  
 91 typedef struct TestDouble_S  
 92 {  
 93     char cOne;  
 94     double dfAlign;  
 95 }TestDouble;  
 96 typedef struct TestDoubleEml_S  
 97 {  
 98     char cOne;  
 99     EightBytesEml dfAlign;  
100 }TestDoubleEml;  
101   
102   
103 // #define _USE_WINDOWS_CE_PLATFORM  
104 void CalcSizeOfStruct(void)  
105 {  
106 #ifdef _USE_WINDOWS_CE_PLATFORM  
107     RETAILMSG(1,(L"size of char is %d\r\n",sizeof(char)));  
108     RETAILMSG(1,(L"size of short is %d\r\n",sizeof(short)));  
109     RETAILMSG(1,(L"size of int is %d\r\n",sizeof(int)));  
110     RETAILMSG(1,(L"size of long is %d\r\n",sizeof(long)));  
111     RETAILMSG(1,(L"size of char * is %d\r\n",sizeof(char *)));  
112     RETAILMSG(1,(L"size of float is %d\r\n",sizeof(float)));  
113     RETAILMSG(1,(L"size of double is %d\r\n",sizeof(double));  
114       
115     // 对比 TestOder, TestOrder3 和 TestOder2 占用内存空间的情况  
116     RETAILMSG(1,(L"size of struct(char,char,int,char,char) is %d\r\n",sizeof(TestOrder)));  
117     RETAILMSG(1,(L"size of struct(int,char,char,char,char) is %d\r\n",sizeof(TestOrder2)));  
118     RETAILMSG(1,(L"size of struct(int,char,char,char) is %d\r\n",sizeof(TestOrder3)));  
119       
120     // 对比 TestShort 和 TestShortEml 占用内存空间的情况  
121     RETAILMSG(1,(L"size of struct(char,short) is %d\r\n",sizeof(TestShort)));  
122     RETAILMSG(1,(L"size of struct(char,TwoBytesEml(char,char)) is %d\r\n",sizeof(TestShortEml)));  
123       
124     // 对比 TestInt 和 TestIntEml 占用内存空间的情况  
125     RETAILMSG(1,(L"size of struct(char,int) is %d\r\n",sizeof(TestInt)));  
126     RETAILMSG(1,(L"size of struct(char,FourBytesEml(char,char,char,char)) is %d\r\n",sizeof(TestIntEml)));  
127       
128     // 对比 TestDouble 和 TestDoubleEml 占用内存空间的情况  
129     RETAILMSG(1,(L"size of struct(char,double) is %d\r\n",sizeof(TestDouble)));  
130     RETAILMSG(1,(L"size of struct(char,EightBytesEml(char,char,char,char,char,char,char,char)) is %d\r\n",  
131         sizeof(TestDoubleEml)));  
132 #else  
133     printf("size of char is %d\r\n",sizeof(char));  
134     printf("size of short is %d\r\n",sizeof(short));  
135     printf("size of int is %d\r\n",sizeof(int));  
136     printf("size of long is %d\r\n",sizeof(long));  
137     printf("size of char * is %d\r\n",sizeof(char *));  
138     printf("size of float is %d\r\n",sizeof(float));  
139     printf("size of double is %d\r\n",sizeof(double));  
140       
141     // 对比 TestOder, TestOrder3 和 TestOder2 占用内存空间的情况  
142     printf("size of struct(char,char,int,char,char) is %d\r\n",sizeof(TestOrder));  
143     printf("size of struct(int,char,char,char,char) is %d\r\n",sizeof(TestOrder2));  
144     printf("size of struct(int,char,char,char) is %d\r\n",sizeof(TestOrder3));  
145       
146     // 对比 TestShort 和 TestShortEml 占用内存空间的情况  
147     printf("size of struct(char,short) is %d\r\n",sizeof(TestShort));  
148     printf("size of struct(char,TwoBytesEml(char,char)) is %d\r\n",sizeof(TestShortEml));  
149       
150     // 对比 TestInt 和 TestIntEml 占用内存空间的情况  
151     printf("size of struct(char,int) is %d\r\n",sizeof(TestInt));  
152     printf("size of struct(char,FourBytesEml(char,char,char,char)) is %d\r\n",sizeof(TestIntEml));  
153       
154     // 对比 TestDouble 和 TestDoubleEml 占用内存空间的情况  
155     printf("size of struct(char,double) is %d\r\n",sizeof(TestDouble));  
156     printf("size of struct(char,EightBytesEml(char,char,char,char,char,char,char,char)) is %d\r\n",  
157         sizeof(TestDoubleEml));  
158 #endif  
159 }  
160   
161   
162 // 第二部分 Leo.Zheng   
163 struct TstStruct  
164 {  
165     char *p;  
166     char c;  
167     long x;  
168 };  
169   
170   
171 struct TstStruct2  
172 {  
173     char c;      /* 1 byte */  
174     char pad[7]; /* 7 bytes */  
175     char *p;     /* 4 bytes */  
176     long x;      /* 4 bytes */  
177 };  
178   
179   
180 struct TstStruct3  
181 {  
182     char *p;     /* 4 bytes */  
183     char c;      /* 1 byte */  
184 };  
185   
186   
187 struct TstStruct4  
188 {  
189     short s;     /* 2 bytes */  
190     char c;      /* 1 byte */  
191 };  
192   
193   
194 struct TstStruct5  
195 {  
196     short s;  
197     char c;  
198     int flip:1;  
199     int nybble:4;  
200     int septet:7;  
201 };  
202   
203   
204 struct TstStruct6  
205 {  
206     char c;  
207     struct Struct6_Sub  
208     {  
209         char *p;  
210         short x;  
211     } inner;  
212 };  
213 struct TstStruct6_R  
214 {  
215     struct Struct6_Sub  
216     {  
217         char *p;  
218         short x;  
219     } inner;  
220     char c;  
221     short s;  
222 };  
223   
224   
225 struct TstStruct7  
226 {  
227     char c;  
228     struct TstStruct7 *p;  
229     short x;  
230 };  
231   
232   
233 struct TstStruct8  
234 {  
235     struct TstStruct8 *p;  
236     short x;  
237     char c;  
238 };  
239   
240   
241 struct TstStruct9  
242 {  
243     struct foo7_inner  
244     {  
245         char *p;  
246         short x;  
247     } inner;  
248     char c;  
249 };  
250   
251   
252 void CalcSizeOfStruct2(void)  
253 {  
254 #ifdef _USE_WINDOWS_CE_PLATFORM  
255     RETAILMSG(1,(L"size of (struct TstStruct)    = %d\n", sizeof(struct TstStruct)));  
256     RETAILMSG(1,(L"size of (struct TstStruct2)   = %d\n", sizeof(struct TstStruct2)));  
257     RETAILMSG(1,(L"size of (struct TstStruct3)   = %d\n", sizeof(struct TstStruct3)));  
258     RETAILMSG(1,(L"size of (struct TstStruct4)   = %d\n", sizeof(struct TstStruct4)));  
259     RETAILMSG(1,(L"size of (struct TstStruct5)   = %d\n", sizeof(struct TstStruct5)));  
260     RETAILMSG(1,(L"size of (struct TstStruct6)   = %d\n", sizeof(struct TstStruct6)));  
261     RETAILMSG(1,(L"size of (struct TstStruct6_R) = %d\n", sizeof(struct TstStruct6_R)));  
262     RETAILMSG(1,(L"size of (struct TstStruct7)   = %d\n", sizeof(struct TstStruct7)));  
263     RETAILMSG(1,(L"size of (struct TstStruct8)   = %d\n", sizeof(struct TstStruct8)));  
264     RETAILMSG(1,(L"size of (struct TstStruct9)   = %d\n", sizeof(struct TstStruct9)));  
265 #else  
266     printf("size of (struct TstStruct)    = %d\n", sizeof(struct TstStruct));  
267     printf("size of (struct TstStruct2)   = %d\n", sizeof(struct TstStruct2));  
268     printf("size of (struct TstStruct3)   = %d\n", sizeof(struct TstStruct3));  
269     printf("size of (struct TstStruct4)   = %d\n", sizeof(struct TstStruct4));  
270     printf("size of (struct TstStruct5)   = %d\n", sizeof(struct TstStruct5));  
271     printf("size of (struct TstStruct6)   = %d\n", sizeof(struct TstStruct6));  
272     printf("size of (struct TstStruct6_R) = %d\n", sizeof(struct TstStruct6_R));  
273     printf("size of (struct TstStruct7)   = %d\n", sizeof(struct TstStruct7));  
274     printf("size of (struct TstStruct8)   = %d\n", sizeof(struct TstStruct8));  
275     printf("size of (struct TstStruct9)   = %d\n", sizeof(struct TstStruct9));  
276 #endif  
277 }  
// 在 WinCE 上运行输出如下:  
/* 
size of char is 1 
size of short is 2 
size of int is 4 
size of long is 4 
size of char * is 4 
size of float is 4 
size of double is 8 
size of struct(char,char,int,char,char) is 12 
size of struct(int,char,char,char,char) is 8 
size of struct(int,char,char,char) is 8 
size of struct(char,short) is 4 
size of struct(char,TwoBytesEml(char,char)) is 3 
size of struct(char,int) is 8 
size of struct(char,FourBytesEml(char,char,char,char)) is 5 
size of struct(char,double) is 16 
size of struct(char,EightBytesEml(char,char,char,char,char,char,char,char)) is 9 
 
 
size of (struct TstStruct)    = 12 
size of (struct TstStruct2)   = 16 
size of (struct TstStruct3)   = 8 
size of (struct TstStruct4)   = 4 
size of (struct TstStruct5)   = 8 
size of (struct TstStruct6)   = 12 
size of (struct TstStruct6_R) = 12 
size of (struct TstStruct7)   = 12 
size of (struct TstStruct8)   = 8 
size of (struct TstStruct9)   = 12 
*/  
// 在 X86 上运行的输出如下：  
/* 
size of char is 1 
size of short is 2 
size of int is 4 
size of long is 4 
size of char * is 4 
size of float is 4 
size of double is 8 
size of struct(char,char,int,char,char) is 12 
size of struct(int,char,char,char,char) is 8 
size of struct(int,char,char,char) is 8 
size of struct(char,short) is 4 
size of struct(char,TwoBytesEml(char,char)) is 3 
size of struct(char,int) is 8 
size of struct(char,FourBytesEml(char,char,char,char)) is 5 
size of struct(char,double) is 16 
size of struct(char,EightBytesEml(char,char,char,char,char,char,char,char)) is 9 
 
 
size of (struct TstStruct)    = 12 
size of (struct TstStruct2)   = 16 
size of (struct TstStruct3)   = 8 
size of (struct TstStruct4)   = 4 
size of (struct TstStruct5)   = 8 
size of (struct TstStruct6)   = 12 
size of (struct TstStruct6_R) = 12 
size of (struct TstStruct7)   = 12 
size of (struct TstStruct8)   = 8 
size of (struct TstStruct9)   = 12 
*/

 

WinCE 下结构体占用空间的分析

标签：

原文地址：http://www.cnblogs.com/91program/p/5205099.html
踩
(0)
赞
(0)
   
举报
评论 一句话评论（0）
登录后才能评论！
分享档案
更多>
2021年07月29日 (22)
2021年07月28日 (40)
2021年07月27日 (32)
2021年07月26日 (79)
2021年07月23日 (29)
2021年07月22日 (30)
2021年07月21日 (42)
2021年07月20日 (16)
2021年07月19日 (90)
2021年07月16日 (35)
周排行
mamicode.com排行更多图片
更多
友情链接
兰亭集智   国之画   百度统计   站长统计   阿里云   chrome插件   新版天听网
关于我们 - 联系我们 - 留言反馈
© 2014 mamicode.com 版权所有  联系我们:gaon5@hotmail.com
迷上了代码！