Thread: K&R Exercise 5-20 : bsearch Error when compiled

Problem

Expand dcl to handle declarations with function argument types, qualifiers like const, and so on.

Answer:
main.c

Code:

#include "extern.h"
#include <string.h>
#include <ctype.h>




enum { NAME, PARENS, BRACKETS};
enum {NO, YES};


void dcl (void);
void dirdcl(void);
void errmsg(char *);
int gettoken(void);


int tokentype;
char token[MAXTOKEN];
char name[MAXTOKEN];
char datatype[MAXTOKEN];
char out[1000];
int prevtoken;


int 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;
}


void dcl (void)
{
    int ns;
    for(ns = 0; gettoken() == '*'; )
        ns++;
    dirdcl();
    while(ns-- > 0)
        strcat(out, " pointer to");
}


void dirdcl(void)
{
    int type;
    void parmdcl(void);
    if(tokentype == '(') {
        dcl();
        if(tokentype != ')')
            errmsg("error: missing )\n");
    } else if (tokentype == NAME) {
        if(name[0] == '\0')
            strcpy(name, token);
    } else
        prevtoken = YES;
    while((type = gettoken()) == PARENS || type == BRACKETS || type == '(')
        if(type == PARENS)
            strcat(out, "function returning");
        else if (type == '(') {
            strcat(out, " function expecting");
            parmdcl();
            strcat(out, " and returning");
        } else {
            strcat(out, " array");
            strcat(out, token);
            strcat(out, " of");
        }
}


void errmsg(char *msg)
{
    printf("%s",msg);
    prevtoken = YES;
}

parmdcl.c

Code:

#include "extern.h"
#include <string.h>
#include <stdlib.h>
#include <ctype.h>


enum { NAME, PARENS, BRACKETS};
enum { NO, YES};


void dcl(void);
void errmsg(char *);
void dclspec(void);
int typespec(void);
int typequal(void);
int compare(char **, char **);
int gettoken(void);


int tokentype;
char token[MAXTOKEN];
char name[MAXTOKEN];
char datatype[MAXTOKEN];
char out[MAXTOKEN];
int prevtoken;


void parmdcl(void)
{
        do {
            dclspec();
        } while(tokentype == ',');
        if(tokentype != ')')
            errmsg("missing ) in parameter declaration\n");
}


void dclspec (void)
{
    char temp[MAXTOKEN];
    temp[0] = '\0';
    gettoken();
    do {
        if (tokentype != NAME) {
            prevtoken = YES;
            dcl();
        } else if (typespec() == YES) {
                strcat(temp, " ");
                strcat(temp, token);
                gettoken();
        } else if(typequal() == YES) {
                strcat(temp, " ");
                strcat(temp, token);
                gettoken();
        } else
            errmsg("unknown type in parameter list \n");
    } while (tokentype != ',' && tokentype != ')');
    strcat(out, temp);
    if(tokentype == ',')
        strcat(out, ",");
}


int typespec(void)
{
    static char *types[] = {
        "char",
        "int",
        "void"
    };
    char *pt = token;
    
    if (bsearch(&pt, types, sizeof(types)/sizeof(char *), sizeof(char *), compare)==NULL)
        return NO;
    else
        return YES;
}


int typequal(void)
{
    static char *typeq[] = {
            "const",
            "volatile"
    };
    char *pt = token;
    
    if(bsearch(&pt, typeq, sizeof(typeq)/sizeof(char *), sizeof(char *), compare) == NULL)
        return NO;
    else
        return YES;
    
}


int compare(char **s, char **t)
{
    return strcmp(*s, *t);
}

gettoken.c

Code:

#include "extern.h"
#include <ctype.h>
#include <string.h>


enum {NAME, PARENS, BRACKETS};
enum {NO, YES};


int tokentype;
char token[MAXTOKEN];
int prevtoken = NO;


int gettoken(void)
{
    int c, getch(void);
    void ungetch(int);
    char *p = token;
    
    if (prevtoken == YES) {
        prevtoken = NO;
        return tokentype;
    }
    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;
}


#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) /* pretend to push character back on input */
{
    if (bufp >= BUFSIZE) 
        printf("ungetch:  too many characters\n");
    else 
        buf[bufp++] = c;
}

extern.h

Code:

#include <stdio.h>
extern int tokentype;
extern char token[];
extern char name[];
extern char datatype[];
extern char out[];
extern int prevtoken;


#define MAXTOKEN 100

gcc main.c parmdcl.c gettoken.c -Wall -Werror -pedantic -g -o dcl.exe
Error: passing argument 5 of 'bsearch' from incompatible pointer type [-Werror]

So i think the 5th argument of bsearch doesn't seem to accept double pointers. The function compare()'s parameter have two double pointers because it will receive string arguments for the bsearch (from <stdlib.h>) to compare them if they are in the static char arrays, *typeq[] and *types[].

The error lies in the functions typespec() and typequal() in the parmdcl.c sourcefile. Anyone know how to make this work?

1. Are you not compiling gettoken.c as well?
2. Why are you redefining your global variables in each of your source files? You know that the linker is going to complain when it has to merge them to build the executable right? If you want to use globals from one file in another file, then you define them extern in a scope visible to all the source files that need access to those globals and then you actually declare them in one (and only one) source file, not multiple source files.
3. The last argument of bsearch function is of type int (*compar)(const void*,const void*), what you give it has to match that expected signature, your compare function does not.

I did what you told me and the code now works. Can you check if what i did was the right thing?

parmdcl.c

Code:

...
int compare(const void *s, const void *t)
{
    char **chs;
    char **cht;
    chs = (char **) s;
    cht = (char **) t;
    return strcmp(*chs, *cht);
}
...

Originally Posted by hk_mp5kpdw

2. Why are you redefining your global variables in each of your source files? You know that the linker is going to complain when it has to merge them to build the executable right? If you want to use globals from one file in another file, then you define themextern in a scope visible to all the source files that need access to those globals and then you actually declare them in one (and only one) source file, not multiple source files.

Is this correct? I redefined them only in the main source file as what you told me to do.
extern.h

Code:

#include <stdio.h>
extern int tokentype;
extern char token[];
extern char name[];
extern char datatype[];
extern char out[];
extern int prevtoken;




enum {NAME, PARENS, BRACKETS};
enum {NO, YES};


#define MAXTOKEN 100

main.c

Code:

...
int tokentype;
char token[MAXTOKEN];
char name[MAXTOKEN];
char datatype[MAXTOKEN];
char out[1000];
...

gettoken.c

Code:

...
int prevtoken = NO;
...

in parmdcl.c i didn't declare any global variables since all of them are already redefined in a source file

Anyway, thanks for all your help. The code now works.