国庆c语言日记（结构）

C编译器对结构空间缺省的分配

　　 在C语言中，结构是一种复合数据类型，其构成元素既可以是基本数据类型（如int、long、float等）的变量，也可以是一些复合数据类型（如数组、结构、联合等等）的数据单元。在结构中，编译器为结构的每个成员按其自然对界（alignment）条件分配空间；各个成员按照它们被声明的顺序在内存中顺序存储，第一个成员的地址和整个结构的地址相同。在缺省情况下，C编译器为每一个变量或是数据单元按其自然对界条件分配空间

例如，下面的结构各成员空间分配情况：
struct test {
char x1;
short x2;
float x3;
char x4;
};
　　
　　　　　　　　　　　　　　　　　
结构的第一个成员x1，其偏移地址为0，占据了第1个字节。第二个成员x2为short类型，其起始地址必须2字节对界，因此，编译器在x2和x1之间填充了一个空字节。结构的第三个成员x3和第四个成员x4恰好落在其自然对界地址上，在它们前面不需要额外的填充字节。在test结构中，成员x3要求4字节对界，是该结构所有成员中要求的最大对界单元，因而test结构的自然对界条件为4字节，编译器在成员x4后面填充了3个空字节。整个结构所占据空间为12字节。

结构中的位段
　　 所谓位段是以位为单位定义长度的结构体类型中的成员。编译器对结构中位段的分配遵从下面几点原则：
? 对于长度为0的位段，其下一个位段从下一个存储单元开始存放：
如：
struct T {
unsigned char a : 1;
unsigned char b : 2;
unsigned : 0;
unsigned c : 3;
};
　　 结构T的成员a和b在一个存储单元中，c则在另一个存储单元中。
　　 · 一个位段必须存储在同一存储单元中，不能跨两个单元：
如：
struct T {
unsigned char a : 4;
unsigned char b : 6;
};
　　 结构T的成员a在一个存储单元中，b则在另一个存储单元中。

更改C编译器的缺省分配策略
　　 一般地，可以通过下面的两种方法改变缺省的对界条件：
　　 · 使用伪指令#pragma pack ([n])
　　 · 在编译时使用命令行参数
#pragma pack ([n])伪指令允许你选择编译器为数据分配空间所采取的对界策略.

　　 在Microsfot Visual C++中，命令行参数/Zp[n]可以改变缺省对界条件；在Borland C++ Builder中，命令行参数-a[n]可以改变缺省对界条件。n的含义和#pragma pack中的n相同。
　　 例如，在使用了#pragma pack (1)伪指令后，test结构各成员的空间分配情况.

 

 

//结构初探 #include<stdio.h>#define MAXTITL 41#define MAXAUTL 31struct book { char title[MAXTITL]; char author[MAXAUTL]; float value; };int main(void){ struct book library; printf("PLease enter the book title/n"); gets(library.title); printf("Now enter the author ./n"); gets(library.author); printf("Now enter the value./n"); scanf("%f",&library.value); printf("%s by %s: $%.2f/n",library.title,library.author,library.value); printf("%s:/"%s/"($%.2f)/n",library.author,library.title,library.value); printf("Done!"); getch(); return 0;}

 

#include<stdio.h>#define MAXTITL 40#define MAXAUTL 40#define MAXBKS 100struct book{ char title[MAXTITL]; char author[MAXAUTL]; float value;};int main(void){ struct book library[MAXBKS]; int count = 0; int index; printf ("Please enter book title./n"); printf ("Press [enter] at the start of a line to stop./n"); while (count < MAXBKS && gets(library[count].title) != NULL && library[count].title[0] != '/0') { printf ("Now enter the author./n"); gets (library[count].author); printf ("Now enter the value./n"); scanf ("%f",&library[count++].value); while (getchar() != '/n') { continue; } if (count < MAXBKS) { printf("Enter the next title./n"); } } if (count > 0) { printf ("Here is the list of your book:/n"); for (index = 0; index < count; index++) { printf ("%s by %s : $ %.2f/n",library[index].title, library[index].author,library[index].value); } } else { printf ("No books? Too bad./n"); } getch(); return 0;}

 

//嵌套结构#include <stdio.h>#define LEN 20const char * msgs[5] ={ "Thank you for the wonderful eveing.", "You certainly prove that a", "is a special kind of guy.We must get together", "over a delicious", " and have a few laughs"};struct names{ char first[LEN]; char last[LEN];};struct guy{ struct names handle; char favfood[LEN]; char job[LEN]; float income;};int main(void){ struct guy fellow = { {"Ewen","Villard"}, "grilled salmon", "personaloty coach", 58112.00 }; printf ("Dear %s./n/n",fellow.handle.first); printf ("%s%s./n",msgs[0],fellow.handle.first); printf ("%s%s/n",msgs[1],fellow.job); printf ("%s/n",msgs[2]); printf ("%s%s%s",msgs[3],fellow.favfood,msgs[4]); if (fellow.income > 150000.0) { puts ("!!"); } else if (fellow.income>75000.0) { puts ("!"); } else { puts ("."); } printf ("/n%40s%s/n"," ","See you soon."); printf ("%40s%s/n"," ","Shalala"); getch(); return 0;}

 

#include<stdio.h>#define LEN 20struct names{ char first[LEN]; char last[LEN];};struct guy{ struct names handles; char favfood[LEN]; char job[LEN]; float income;};int main(void){ struct guy fellow[2] = { { {"Ewen","villard"}, "grilled salmon", "personality coach", 58112.00 }, { {"Rodney","Swillbelly"}, "tripe", "tabloid editor", 232400.00 } }; struct guy * him;/*指向结构的指针*/ printf ("address #1:%p #2: %p/n",&fellow[0],&fellow[1]); him = &fellow[0];/*告诉该指针要指向的地址*/ printf ("pointer #1:%p #2:%p/n",him,him+1); printf("him->income is $%.2f:(*him).income is $%.2f/n", him->income,(*him).income); him++;/*指向下一个结构*/ printf("him->favfood is %s: him->handle.last is %s/n", him->favfood,him->handles.last); getch(); return 0; }

 

 

 

//传递结构#include <stdio.h>#define FUNDLEN 50struct funds{ char bank[FUNDLEN]; double bankfund; char save[FUNDLEN]; double savefund;};double sum (double,double);int main(void){ struct funds stan = { "Garlic-Melon Bank", 3024.72, "Lucky's Savings and :oan", 9237.11 }; printf ("Stan has a total of $%.2f./n", sum(stan.bankfund,stan.savefund)); getch(); return 0; } double sum (double x, double y){ return(x+y);}

 

//传递指向结构的指针#include <stdio.h>#define FUNDLEN 50struct funds{ char bank[FUNDLEN]; double bankfund; char save[FUNDLEN]; double savefund;};double sum(const struct funds *);int main(void){ struct funds stan = { "Garlic-Melon Bank", 3024.43, "Lucky's Saving and Loan", 9237.11 }; printf("Stan has a total of $%.2f/n",sum(&stan)); return 0;} double sum(const struct funds * money){ return(money->bankfund + money->savefund);}

 

//使用指向结构的指针#include <stdio.h>#include <string.h>struct namect{ char fname[20]; char lname[20]; int letters;};void getinfo (struct namect *);void makeinfo (struct namect *);void showinfo (const struct namect *);int main(void){ struct namect person; getinfo (&person); makeinfo (&person); showinfo (&person); getch(); return 0;}void getinfo (struct namect *pst){ printf("Please enter yout first name./n"); gets(pst->fname); printf("Please enter yout last name./n"); gets(pst->lname);}void makeinfo(struct namect *pst){ pst->letters = strlen(pst->fname) + strlen(pst->lname); }void showinfo (const struct namect *pst){ printf("%s %s,your name contains %d letters./n", pst->fname, pst->lname, pst->letters);} //使用指针和malloc（）函数#include<stdio.h>#include<string.h>//使用strcpy（），strlen（） #include<stdlib.h>//使用malloc（），free（） struct namect{ char * fname; char * lname; int letters;};void getinfo(struct namect *);//分配内存 void makeinfo(struct namect *);void showinfo(const struct namect *);void cleanup(struct namect *);//释放内存int main(void){ struct namect person; getinfo (&person); makeinfo (&person); showinfo (&person); cleanup (&person); getch(); return 0;}void getinfo (struct namect *pst){ char temp[81]; printf("Please enter your first name./n"); gets(temp); pst->fname = (char *)malloc(strlen(temp)+1); strcpy(pst->fname,temp); printf("Please enter your last name./n"); gets(temp); pst->lname = (char *)malloc(strlen(temp) + 1); strcpy(pst->lname,temp);}void makeinfo(struct namect *pst){ pst->letters = strlen(pst->fname) + strlen(pst->lname);}void showinfo (const struct namect * pst){ printf("%s %s,your name contains %d letters./n", pst->fname,pst->lname,pst->letters);}void cleanup(struct namect *pst){ free(pst->fname); free(pst->lname);}

 

 

#include<stdio.h>#include<string.h>struct namect{ char fname[20]; char lname[20]; int letters;};struct namect getinfo(void);struct namect makeinfo(struct namect);void showinfo (struct namect);int main(void){ struct namect person; person = getinfo(); person = makeinfo(person); showinfo(person); getch(); return 0;}struct namect getinfo(void){ struct namect temp; printf("Please enter your first name./n"); gets(temp.fname); printf("Please enter your lasr name./n"); gets(temp.lname); return temp;}struct namect makeinfo (struct namect info){ info.letters = strlen(info.fname)+strlen(info.lname); return info;}void showinfo(struct namect info){ printf("%s %s,your name contains %d letters,/n", info.fname,info.lname,info.letters);}