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@YieldNull
Created November 1, 2015 12:44
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Recognize C Pointer Declaration(识别C语言指针表达式)
/*
* R2LParser.c
*
* Recognize C declaration use Right-Left Method(from http://ieng9.ucsd.edu/~cs30x/rt_lt.rule.html)
*
* The "right-left" rule is a completely regular rule for deciphering C
* declarations. It can also be useful in creating them.
*
* First, symbols. Read
* * as "pointer to" - always on the left side
* [] as "array of" - always on the right side
* () as "function returning" - always on the right side
*
* as you encounter them in the declaration.
*
* STEP 1
* ------
* Find the identifier. This is your starting point. Then say to yourself,
* "identifier is." You've started your declaration.
*
* STEP 2
* ------
* Look at the symbols on the right of the identifier. If, say, you find "()"
* there, then you know that this is the declaration for a function. So you
* would then have "identifier is function returning". Or if you found a
* "[]" there, you would say "identifier is array of". Continue right until
* you run out of symbols *OR* hit a *right* parenthesis ")". (If you hit a
* left parenthesis, that's the beginning of a () symbol, even if there
* is stuff in between the parentheses. More on that below.)
*
* STEP 3
* ------
* Look at the symbols to the left of the identifier. If it is not one of our
* symbols above (say, something like "int"), just say it. Otherwise, translate
* it into English using that table above. Keep going left until you run out of
* symbols *OR* hit a *left* parenthesis "(".
*
*
* Created on: Sep 23, 2015
* Author: hejunjie.net
*/
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#define MAXLENGTH 100 // the max length of a token
#define BUFSIZE 100 // buffer size
/* user defined token type */
enum {
NAME, PARENTS, BRACKETS
};
int tokentype; // token type: NAME, PARENTS, BRACKETS or '\n' etc.
char token[MAXLENGTH];// name, pair of parentheses, pair of brackets perhaps including a number, or other single character
char name[MAXLENGTH]; // identifier name
char datatype[MAXLENGTH]; //char int double etc.
char out[1000]; //output string
void dcl(void); // consume a declaration
void dirdcl(void); // consume a direct declaration
int gettoken(void); // read a token from input
/* look ahead mechanism*/
char buf[BUFSIZE]; // buffer to store look ahead char
int bufp = 0; // next free position in buffer
int getch(); // read a char from input or buffer
void ungetch(int c); // push char to buffer
int main(void) {
while (gettoken() != EOF) { // each loop parse one line
strcpy(datatype, token);
out[0] = '\0';
dcl();
if (tokentype != '\n')
printf("syntax error\n");
printf("%s: %s %s\n", name, out, datatype);
}
return 0;
}
void dcl(void) {
int count = 0;
while (gettoken() == '*') {
count++;
}
dirdcl();
while (count-- > 0) {
strcat(out, " pointer to");
}
}
void dirdcl(void) {
int type;
if (tokentype == '(') {
dcl();
if (tokentype != ')') {
printf("error: missing )\n");
}
} else if (tokentype == NAME) {
strcpy(name, token);
} else {
printf("error: expected name or (dcl)\n");
}
while ((type = gettoken()) == PARENTS || type == BRACKETS) {
if (type == PARENTS) {
strcat(out, " function returning");
} else {
strcat(out, " array ");
strcat(out, token);
strcat(out, " of");
}
}
}
/*read token from input to 'token' array and return token type*/
int gettoken(void) {
int c;
char *p = token;
// consume white char
while ((c = getch()) == ' ' || c == '\t')
;
if (c == '(') { // consume parentheses
if ((c = getch()) == ')') {
strcpy(token, "()");
return tokentype = PARENTS;
} else {
ungetch(c);
return tokentype = '(';
}
} else if (c == '[') { // consume brackets
for (*p++ = c; (*p++ = getch()) != ']';)
;
*p = '\0';
return tokentype = BRACKETS;
} else if (isalpha(c)) { // consume identifier
for (*p++ = c; isalnum(c = getch());) {
*p++ = c;
}
*p = '\0';
ungetch(c);
return tokentype = NAME;
} else {
return tokentype = c;
}
}
int getch(void) {
// read char from input or buffer if there exists data
return (bufp > 0) ? buf[--bufp] : getchar();
}
void ungetch(int c) {
// push 'dirty' char back to buffer
if (bufp >= BUFSIZE)
printf("ungetch: too many characters!");
else
buf[bufp++] = c;
}
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