How do I read this declaration?
I'm trying to apply operator precedence to unravel it, but the outer void and (int) are really throwing me off.Code:void (*signal(int sig, void (*handler)(int)))(int)
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How do I read this declaration?
I'm trying to apply operator precedence to unravel it, but the outer void and (int) are really throwing me off.Code:void (*signal(int sig, void (*handler)(int)))(int)
sig is an int.
handler is a pointer to a function that takes an int and returns a void.
signal is a function that takes sig and handler as parameters, and returns a pointer. That pointer, when dereferenced, is a function takes an (unnamed) int parameter and returns void. (I think. I may have gotten a pointer and a function turned around.)
Here's a breakdown of the function, much easier to see and understand because someone neglected to create readable code (:rolleyes:):
typedef void (handler_t)(int);
typedef void (signal_return_t)(int);
signal_return_t* signal(int sig, handler_t* handler);
There's actually a program in The C Programming Language that splits declarations like this . . . it starts on page 90 of this: http://www.ica.luz.ve/dfinol/tpro/kandr.pdf
Since that's probably an illegal copy of the book, I've copied the code here for you:
It doesn't work as well I remember it doing . . . I must have improved it, but I can't find where I put my version. :)Code:/* From The C Programming Language */
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#define BUFSIZE 100
char buf[BUFSIZE]; /* buffer for ungetch */
int bufp = 0; /* next free position in buf */
int getch(void) /* get a (possibly pushed-back) character */
{
return (bufp > 0) ? buf[--bufp] : getchar();
}
void ungetch(int c) /* push character back on input */
{
if (bufp >= BUFSIZE)
printf("ungetch: too many characters\n");
else
buf[bufp++] = c;
}
#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];
main() /* convert declaration to words */
{
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");
}
}
int gettoken(void) /* return next token */
{
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;
}