CODEWITHSUNDEEP
cstruct
Denis Steinman
Denis Steinman

Reputation: 7799

invalid type argument of ‘->’ (have ‘fd_set’)

I know it's not the first thread with this error but I really can't get what's wrong... My code is bellow: 

/* File descriptor sets */
struct descs {
    fd_set read;
    fd_set write;
    fd_set except;
};

typedef struct descs descs_t;

/* Server representation */
struct server {
    int                 sock;                   /* Server sock descriptor */
    struct sockaddr_in  addr;                   /* Server address */
    socklen_t           addrlen;                /* Server address size */
    char                buffer[BUFFER_SIZE];    /* Message buffer */
    int                 len;                    /* Message buffer length */
};

typedef struct server server_t;

void build_fds(struct server *srv, struct descs *fd) {
    FD_ZERO(fd->read);
    FD_SET(STDIN_FILENO, fd->read);
    FD_SET(srv->sock, fd->read);

    FD_ZERO(fd->write);
    // there is smth to send, set up write_fd for server socket
    if (srv->len > 0) {
        FD_SET(srv->sock, fd->write);
    }

    FD_ZERO(fd->except);
    FD_SET(STDIN_FILENO, fd->except);
    FD_SET(srv->sock, fd->except);
}

I am passing my struct via pointer so I must use -> but it crashes with errors: 

chatcl.c: In function ‘build_fds’:
chatcl.c:37: error: invalid type argument of ‘->’ (have ‘fd_set’)
chatcl.c:38: error: invalid type argument of ‘->’ (have ‘fd_set’)
chatcl.c:39: error: invalid type argument of ‘->’ (have ‘fd_set’)
chatcl.c:41: error: invalid type argument of ‘->’ (have ‘fd_set’)
chatcl.c:44: error: invalid type argument of ‘->’ (have ‘fd_set’)
chatcl.c:47: error: invalid type argument of ‘->’ (have ‘fd_set’)
chatcl.c:48: error: invalid type argument of ‘->’ (have ‘fd_set’)
chatcl.c:49: error: invalid type argument of ‘->’ (have ‘fd_set’)
make: *** [chatcl] Error 1

What's wrong in my code?

Upvotes: 1

Views: 924

Answers (2)

Stefan Becker
Stefan Becker

Reputation: 5962

You are missing the &, i.e. you need the address of the data structure, e.g.

#include <sys/select.h>

struct descs {
  fd_set a;
};

void func(struct descs *d) {
  FD_ZERO(&d->a);
}

Upvotes: 3

KamilCuk
KamilCuk

Reputation: 141235

From man select the FD_* macros they take pointers to fd_set:

   void FD_CLR(int fd, fd_set *set);
   int  FD_ISSET(int fd, fd_set *set);
   void FD_SET(int fd, fd_set *set);
   void FD_ZERO(fd_set *set);

You should pass pointers to the functions (macros), not values. You can use the address-of operator:

FD_ZERO(&fd->read);
FD_SET(STDIN_FILENO, &fd->read);
FD_SET(srv->sock, &fd->read);

and so on.

Upvotes: 2

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