dcl--complicated declarations
#include <stdio.h>
#include <string.h> //for strcpy(), strcat()
#include <ctype.h> //for isalpha(), isalnum()
//compile with: gcc -Wall -Wextra cc-c.c -o cc-c
//run with: printf 'char **argv\n' | ./cc-c # argv: pointer to pointer to char
// or: printf 'int (*daytab)[13]\n' | ./cc-c # daytab: pointer to array[13] of int
// or: printf 'int *daytab[13]\n' | ./cc-c # daytab: array[13] of pointer to int
// or: printf 'void (*comp)()\n' | ./cc-c # comp: pointer to function returning void
// or: printf 'char (*(*x())[])()\n' | ./cc-c # x: function returning pointer to array[] of pointer to function returning char
// or: printf 'char (*(*x[3])())[5]\n' | ./cc-c # x: array[3] of pointer to function returning pointer to array[5] of char
//K&R2 section 5.12: complicated declarations. dcl reads a C
//declaration and says it in words:
//
// char (*(*x())[])() -> x: function returning pointer to array[]
// of pointer to function returning char
//
//The grammar it follows (from the book):
//
// dcl: optional *'s direct-dcl
// direct-dcl: name
// ( dcl )
// direct-dcl ()
// direct-dcl [optional size]
//
//In words: a declarator is some *'s in front of a direct declarator;
//a direct declarator is a name, or a whole declarator in parentheses,
//followed by any number of () and [] suffixes.
//
//dcl and dirdcl call EACH OTHER -- dcl calls dirdcl, and dirdcl calls
//dcl again when it meets "(". This is "recursive descent": one
//function per grammar rule, and the program's call stack mirrors the
//nesting of parentheses in the declaration.
//
//Why the words come out in the right order: dcl COUNTS its *'s first,
//lets dirdcl handle everything to the right (name, (), []), and only
//then appends " pointer to" once per *. So in *x[3], "array[3] of"
//is written before "pointer to" -- matching C's rule that [] and ()
//bind tighter than *.
//
//The book's own warnings (from the Chinese edition's text): dcl is
//deliberately simple. It handles only simple data types like char or
//int -- not argument types inside (), and not qualifiers like const.
//Unneeded blanks confuse it, and it has no error recovery, so an
//invalid declaration can throw it off. Fixing these is left to the
//exercises (5-18 to 5-20).
//
//Fixed from the book's text: main() -> int main(void). gcc 15 defaults
//to C23, which no longer allows a function without a return type.
#define MAXTOKEN 100
enum { NAME, PARENS, BRACKETS };
void dcl(void);
void dirdcl(void);
int gettoken(void);
int tokentype; //type of last token
char token[MAXTOKEN]; //last token string
char name[MAXTOKEN]; //identifier name
char datatype[MAXTOKEN]; //data type = char, int, etc.
char out[1000];
//convert declaration to words
int main(void)
{
while (gettoken() != EOF) { //1st token on line
strcpy(datatype, token); //is the datatype
out[0] = '\0';
dcl(); //parse rest of line
if (tokentype != '\n')
printf("syntax error\n");
printf("%s: %s %s\n", name, out, datatype);
}
return 0;
}
//dcl: parse a declarator
void dcl(void)
{
int ns;
for (ns = 0; gettoken() == '*'; ) //count *'s
ns++;
dirdcl();
while (ns-- > 0)
strcat(out, " pointer to");
}
//dirdcl: parse a direct declarator
void dirdcl(void)
{
int type;
if (tokentype == '(') { //( dcl )
dcl();
if (tokentype != ')')
printf("error: missing )\n");
} else if (tokentype == NAME) //variable name
strcpy(name, token);
else
printf("error: expected name or (dcl)\n");
while ((type=gettoken()) == PARENS || type == BRACKETS)
if (type == PARENS)
strcat(out, " function returning");
else {
strcat(out, " array");
strcat(out, token);
strcat(out, " of");
}
}
//gettoken: return next token
int gettoken(void)
{
int c, getch(void);
void ungetch(int);
char *p = token;
while ((c = getch()) == ' ' || c == '\t')
;
if (c == '(') {
if ((c = getch()) == ')') {
strcpy(token, "()");
return tokentype = PARENS;
} else {
ungetch(c);
return tokentype = '(';
}
} else if (c == '[') {
for (*p++ = c; (*p++ = getch()) != ']'; )
;
*p = '\0';
return tokentype = BRACKETS;
} else if (isalpha(c)) {
for (*p++ = c; isalnum(c = getch()); )
*p++ = c;
*p = '\0';
ungetch(c);
return tokentype = NAME;
} else
return tokentype = c;
}
//--- from section 4.3 ---
#define BUFSIZE 100
char buf[BUFSIZE]; //buffer for ungetch
int bufp = 0; //next free position in buf
//getch: get a (possibly pushed back) character
int getch(void)
{
return (bufp > 0) ? buf[--bufp] : getchar();
}
//ungetch: push character back on input
void ungetch(int c)
{
if (bufp >= BUFSIZE)
printf("ungetch: too many characters\n");
else
buf[bufp++] = c;
}
win@DESKTOP-MEIH88T:~$ cd webdev-projects win@DESKTOP-MEIH88T:~/webdev-projects$ gcc -Wall -Wextra cc-c.c -o cc-c win@DESKTOP-MEIH88T:~/webdev-projects$ printf 'char **argv\n' | ./cc-c argv: pointer to pointer to char win@DESKTOP-MEIH88T:~/webdev-projects$ printf 'int (daytab)[13]\n' | ./cc-c daytab: pointer to array[13] of int win@DESKTOP-MEIH88T:~/webdev-projects$ printf 'int daytab[13]\n' | ./cc-c daytab: array[13] of pointer to int win@DESKTOP-MEIH88T:~/webdev-projects$ printf 'void (comp)()\n' | ./cc-c comp: pointer to function returning void win@DESKTOP-MEIH88T:~/webdev-projects$ printf 'char ((x())[])()\n' | ./cc-c x: function returning pointer to array[] of pointer to function returning char win@DESKTOP-MEIH88T:~/webdev-projects$ printf 'char ((*x[3])())[5]\n' | ./cc-c x: array[3] of pointer to function returning pointer to array[5] of char win@DESKTOP-MEIH88T:~/webdev-projects$ printf 'int x)\n' | ./cc-c syntax error x: int error: expected name or (dcl) syntax error x: x
You can also read declarations by hand with the right-left rule. Start at the name, go right while you can, go left when you hit ), and repeat:
char (*(*x[3])())[5]
x x is
[3] array[3] of
* pointer to
() function returning
* pointer to
[5] array[5] of
char char
That's the same order dcl produces, because dcl is this rule written as code.
char **argv argv: pointer to char int (daytab)[13] daytab: pointer to array[13] of int int daytab[13] daytab: array[13] of pointer to int void comp() comp: function returning pointer to void void (comp)() comp: pointer to function returning void char ((x())[])() x: function returning pointer to array[] of pointer to function returning char char ((x[3])())[5] x: array[3] of pointer to function returning pointer to arra