TCPL——练习6.5 & 6.6

　　这两道习题综合起来是利用散列表写个适用C语言的简单#define处理器，只能处理#define/#undef不带参数的情形，并且#define后面必须带值。不带值其实也就是加多一个处理，分辨#define语句是否已经结束。这里输入代码我用的是TCPL的getch, ungetch，其实本应该直接读入一个C文件，可是这里我偷懒了。读入文件的话处理代码差别也不大。我把代码分为几个模块：

hash.c：散列表相关代码

io.c：输入输出相关代码

main.c：测试

　　以下是代码hash.h：保留三个借口给其他模块调用

#ifndef HASH_H
#define HASH_H

struct nlist;

struct nlist *install(char *name, char *defn);
int undef(char *name);
void print(void);

#endif

散列表实现文件：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct nlist {
    char *name;                /* defined name        */
    char *defn;                /* replaced value    */
    struct nlist *next;        /* next node        */
};

#define HASHSIZE 101
static struct nlist *hashtab[HASHSIZE];

void print(void)
{
    struct nlist *np;
    for (int i = 0; i < HASHSIZE; ++i) {
        if (hashtab[i] != NULL) {
            for (np = hashtab[i]; np != NULL; np = np->next) {
                printf("name: %-10s  defn: %-5s\n", np->name, np->defn);
            }
        }
    }
}

static char *strdup(char *s)
{
    char *p;

    p = (char *)malloc(strlen(s) + 1);
    if (p != NULL) {
        strcpy(p, s);
    }
    return p;
}

static unsigned int hash(char *s)
{
    unsigned int hashval;

    for (hashval = 0; *s != '\0'; ++s) {
        hashval = *s + 31 * hashval;
    }
    return hashval % HASHSIZE;
}

static struct nlist *lookup(char *s)
{
    struct nlist *np;

    for (np = hashtab[hash(s)]; np != NULL; np = np->next) {
        if (strcmp(s, np->name) == 0) {
            return np;
        }
    }
    return NULL;
}

struct nlist *install(char *name, char *defn)
{
    struct nlist *np;
    unsigned int hashval;

    if ( (np = lookup(name)) == NULL) {
        np = (struct nlist *)malloc(sizeof(struct nlist));
        if (np == NULL || (np->name = strdup(name)) == NULL) {
            return NULL;
        }

        hashval = hash(name);
        np->next = hashtab[hashval];
        hashtab[hashval] = np;
    } else {
        free( (void *)np->defn);        /* free the prev defn */
    }
    if ( (np->defn = strdup(defn)) == NULL) {
        return NULL;
    }
    return np;
}

int undef(char *name)
{
    struct nlist *prev, *np;
    unsigned int hashval;

    if ( (np = lookup(name)) != NULL) {
        hashval = hash(name);
        prev = hashtab[hashval];
        if (prev == np) {
            printf("only one node\n");
            free(np->defn);
            free(np->name);
            free(np);
        } else {
            printf("more than one node\n");
            for ( ; prev->next != np; prev = prev->next)
                ;
            prev->next = np->next;
            free(np->defn);
            free(np->name);
            free(np);
        }
        return 0;
    }  

    return -1;
}

io.h: 只保留一个借口给main函数调用：

#ifndef IO_H
#define IO_H

int getword(char *word, int lim);

#endif

io.c : 输入输出实现文件：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

#define BUFSIZE 100

char buf[BUFSIZE];
int bufp = 0;

int getch(void)
{
    return bufp > 0 ? buf[--bufp] : getchar();
}

void ungetch(int c)
{
    if (bufp >= BUFSIZE) {
        printf("buffer is full.\n");
    }
    buf[bufp++] = c;
}

int getword(char *word, int lim)
{
    int c;
    char *w;

    memset(word, 0x00, lim);
    w = word;

    while (isspace(c = getch()) )
        ;
    if (c != EOF) {
        *w++ = c;
    } else {
        return c;
    }

    for ( ; --lim > 0; w++) {
        if (!isalnum(*w = getch()) ) {
            ungetch(*w);
            break;
        }
    }
    *w = '\0';
    return word[0];
}

最后是main.c文件，调试信息我都去掉了。

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "io.h"
#include "hash.h"

typedef enum _status {
    NONE,
    GET_NAME,
    GET_VALUE,
    UNGET_NAME
} Status;

#define MAXSIZE 100
int main(void)
{
    struct nlist *np;
    Status status = NONE;
    char word[MAXSIZE] = {0};
    char name[MAXSIZE] = {0};
    char defn[MAXSIZE] = {0};

    while (getword(word, MAXSIZE) != EOF) {
        if (strcmp(word, "#define") == 0) {
            status = GET_NAME;
            continue;
        } else if (strcmp(word, "#undef") == 0) {
            status = UNGET_NAME;
            continue;
        } 

        if (status == GET_NAME) {
            memset(name, 0x00, sizeof(name));
            strcpy(name, word);
            status = GET_VALUE;
        } else if (status == GET_VALUE) {
            memset(defn, 0x00, sizeof(defn));
            strcpy(defn, word);
            status = NONE;

            if ( (np = install(name, defn)) == NULL) {
                return -1;
            }
        } else if (status == UNGET_NAME) {
            undef(word);
        }
    }
    print();

    return 0;
}

简单测试结果：

ken@Linux:~/TCPL/chap6/hash$ ./main 
#include <stdio.h>

#define A 100
#define B 200
#define C 300

#undef A
in #undef.
only one node
name:             defn:      
name: B           defn: 200  
name: C           defn: 300