本文主要是介绍C //练习 6-1 上述getword函数不能正确处理下划线、字符串常量、注释及预处理控制指令。请编写一个更完善的getword函数。，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
C程序设计语言 （第二版） 练习 6-1
练习 6-1 上述getword函数不能正确处理下划线、字符串常量、注释及预处理控制指令。请编写一个更完善的getword函数。
注意：代码在win32控制台运行，在不同的IDE环境下，有部分可能需要变更。
IDE工具：Visual Studio 2010
代码块：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>#define MAXWORD 100
#define NKEYS (sizeof keytab / sizeof(keytab[0]))
#define MAXOP 100
#define NUMBER '0'
#define MAXVAL 100
#define BUFSIZE 100
#define VAR '1'char buf[BUFSIZE];
int bufp = 0;struct key{char *word;int count;
};int getch(void){return (bufp > 0) ? buf[--bufp] : getchar();
}void ungetch(int c){if(bufp >= BUFSIZE){printf("Ungetch! Too many characters!\n");}else{buf[bufp++] = c;}
}int getword(char *word, int lim) {int c;char *w = word;static int line_beg = 1; /* 1 at beginning of a new line */static int after_slash = 0; /* 1 after '\' */int after_star = 0; /* 1 after '*' */if(isspace(c = getch()))after_slash = 0;while(isspace(c)) {if(c == '\n')line_beg = 1;c = getch();}if(c != EOF)*w++ = c;if(c == '#' && line_beg == 1) { /* Preprocessor directive */while((c = getch()) != '\n' && c != EOF) /* Go to end of line */;return getword(word, lim); /* Start over */}line_beg = 0;if(c == '\\') /* Set after_slash flag */after_slash = after_slash ? 0 : 1; /* Ignore '\\' comment */else if(c == '/' ) {if((c = getch()) == '*' && !after_slash) { /* Begin comment */while((c = getch()) != EOF) {if(c == '/') {if(after_star) /* End comment */return getword(word, lim); /* Start over */}else if(c == '*' && !after_slash)after_star = 1;else if(c == '\\')after_slash = after_slash ? 0 : 1; /* Ignore '\\' comments */else {after_star = 0;after_slash = 0;}}} /* End comment */after_slash = 0; /* Not after slash anymore */if(c != EOF)ungetch(c);}else if(c == '\"') {if(!after_slash) { /* String literal */--w; /* Reset w */while((c = getch()) != EOF) {if(c == '\"' && !after_slash)break;else if(c == '\\')after_slash = after_slash ? 0 : 1; /* Ignore '\\' comments */elseafter_slash = 0;*w++ = c;}*w = '\0';if(c == EOF)return EOF;elsereturn getword(word, lim); /* Start over. */}after_slash = 0; /* Not after a slash anymore. */}if(!isalpha(c) && c != '_') { /* It's a symbol. */*w = '\0';if(c != '\\')after_slash = 0;return c;}/* Reset this flag since a slash would have just returned. */after_slash = 0;for( ; --lim > 0; ++w) /* It's a word or letter. */if(!isalnum(*w = getch()) && *w != '_') {ungetch(*w);break;}*w = '\0';return word[0];}int binsearch(char *word, struct key tab[], int n){int cond;int low, high, mid;low = 0;high = n - 1;while(low <= high){mid = (low + high) / 2;if((cond = strcmp(word, tab[mid].word)) < 0){high = mid - 1;}else if(cond > 0){low = mid + 1;}else{return mid;}}return -1;
}int main(){struct key keytab[] = {{"auto", 0}, {"break", 0}, {"case", 0}, {"char", 0}, {"const", 0}, {"continue", 0}, {"default", 0},{"do", 0}, {"double", 0}, {"else", 0}, {"enum", 0}, {"extern", 0}, {"float", 0}, {"for", 0}, {"goto", 0}, {"if", 0}, {"int", 0},{"long", 0}, {"register", 0}, {"return", 0}, {"short", 0}, {"signed", 0}, {"sizeof", 0}, {"static", 0}, {"struct", 0}, {"switch", 0},{"typedef", 0}, {"unsigned", 0}, {"union", 0}, {"void", 0}, {"volatile", 0}, {"while", 0}};int n;char word[MAXWORD];while(getword(word, MAXWORD) != EOF){if(isalpha(word[0])){if((n = binsearch(word, keytab, NKEYS)) >= 0){keytab[n].count++;}}}for(n = 0; n < NKEYS; n++){if(keytab[n].count > 0){printf("%4d %s\n", keytab[n].count, keytab[n].word);}}system("pause");return 0;
}
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