NAME

SYNOPSIS

#include <libdillimpl.h>
void* hquery(
    int h,
    const char* type);

    

DESCRIPTION

The type argument is not interpreted in any way. It is used only as an unique ID. A unique ID can be created, for instance, like this:

int foobar_placeholder = 0;
const void *foobar_type = &foobar_placeholder;

    

The return value has no specified semantics. It is an opaque pointer. One typical use case for it is to return a pointer to a table of function pointers. These function pointers can then be used to access the handle's functionality (see the example).

Pointers returned by hquery are meant to be cachable. In other words, if you call hquery on the same handle with the same type multiple times, the result should be the same.

h: The handle.

type: The opaque ID of the queried type.

RETURN VALUE

ERRORS

•

EBADF: Invalid handle.

EXAMPLE

struct quux_vfs {
    int (*foo)(struct quux_vfs *vfs, int a, int b);
    void (*bar)(struct quux_vfs *vfs, char *c);
};
int quux_foo(int h, int a, int b) {
    struct foobar_vfs *vfs = hquery(h, foobar_type);
    if(!vfs) return -1;
    return vfs->foo(vfs, a, b);
}
void quux_bar(int h, char *c) {
    struct foobar_vfs *vfs = hquery(h, foobar_type);
    if(!vfs) return -1;
    vfs->bar(vfs, c);
}

    

SEE ALSO