The C programing language chapter 6 : struct

the chap6 struct

1. basics of structures

//1. define a struct 
way 1：struct point {
    int x;
    int y;
};
way 2：struct point {
    int x;
    int y;
}p_test, *p_pointer;
way 3：struct {
    int x;
    int y;
}point; //this point just only a variale such as a from statement : int a; 
/*this define a struct point that is similar  type int 
declare a struct point variable such as :*/
//2. declare a struct
struct point p1, p2; //just like declare a normal variable except add precedence  struct 

//3. initialize struct variable p1
way 1 : p1.x = 1;
        p1.y = 2;
way 2 : define and initialize
struct point p1 = {1, 2};

//4. struct of pointer,and handle it's members(x, y)
struct point *p;
p = &p1;
p ->x = 4;
p ->y = 5;

2. structures and functions

//1. return a pointer to struct point 
struct point makepoint(int x, int y)
{
    struct point temp;
    temp.x = x;
    temp.y = y;
    return temp;
}

3. arrays of structures

//declare array of struct just like char test[10];
struct point pointTable[100]; 

4. pointers to structures

struct point *p_test; //p_test is pointer to the struct point

5. self-referential structures

//define a tree node
struct tnode {
    char *value;
    struct tnode *left;
    struct tnode *right;
}

6. table lookup

struct nlist {
    struct nlist *next; //the next pointer to the next ectry
    char *name;
}

struct nlist *nlistTab[100];//just like pointer array

7. typedef

//typedef for creating new data type names. for example ,the declaration
typedef int _int;
typedef char *string;
typedef struct tnode *tnode_pointer;
typedef struct tnode {
    char *value;
    tnode_pointer left;
    tnode_pointer right;
}Treenode; //creating two type : tnode_pointer and Treenode

8. unions

union {
    int ival;
    float fval;
    char *sval;
} u;
union u_tay {
    int ival;
    float fval;
    char *sval;
};
union u_tay {
    int ival;
    float fval;
    char *sval;
} u;

9. bit-fields

struct {
    unsigned int is_keyword : 1; //is_keyword width is 1 that maining the it's size is 1 bit
    unsigned int is_extern : 1;
    unsigned int is_static : 1;
} flags;
flags.is_keyword = 1;

#ifndef STDFSH
#define STDFSH 1
#include "stdfs.h"
#endif
/* 有一点我就很疑惑，对注释和字符串的处理，是保存还是忽略不管呢 因为上一个getword是忽略了\/**\/ 和 “” 这个些符号之后会继续处理 他们里面的内容,所以我这里就是忽略到他们里面的内容，其余的几个课后题 我发现理解不了，然后去看答案，发现和题目也不是很对照啊，所以就留着 以后有空在解决把，就把书上的tree的搞一个就可以了。 getword : get next word or character from input */
extern int getch();
extern void ungetch(int c);
int getword(char *word, int lim)
{
    int c, temp;
    char *w = word;
    while (isspace(c = getch()))
        ;
    if (c != EOF)    
    *w++ = c;

    if (isalpha(c) || c == '_' || c == '#')
        for ( ;--lim > 0; ) {
            *w++ = c = getch();
            if (!isalnum(c) && c != '_') {
               ungetch(c);
                break;
            }   
    }
    else if (c == '\'' || c == '"') { 
        for ( ;temp = getch() ; )
            if (temp == c || temp == EOF) 
                break;
        }
    else if (c == '/') {            
        if ((temp = getch()) == '*') {
            for ( ;temp = getch(); )
                if (temp == EOF || temp == '*' && getch() == c)
                    break;
        } else 
            ungetch(temp);
    }
     *--w = '\0';
    if (temp == EOF)
        return EOF;
    return c;    
}
int comment()
{
    int c;
    while (c=getch() != EOF)
        if (c == '*')
            if ((c = getch()) == '/')
               break;
            else
                ungetch(c);
    return c;

}