expected struct foo* but argument is of type struct foo* for function pointers

Question

I have two typedefs for function pointers and two structs, struct pipe_s and struct pipe_buffer_s defined as so:

typedef void (*pipe_inf_t)(struct pipe_buffer_s *);
typedef void (*pipe_outf_t)(struct pipe_buffer_s *);

struct
pipe_buffer_s
{
    size_t cnt;      /* number of chars in buffer */
    size_t len;      /* length of buffer */
    uint8_t *mem;    /* buffer */
};

struct
pipe_s
{
    struct pipe_buffer_s buf;
    uint8_t state;
    pipe_inf_t in;   /* input call */
    pipe_outf_t out; /* output call */
};

In my implementation, I have a function that attempts to call the function in:

void
pipe_receive(struct pipe_s *pipe)
{
    pipe_inf_t in;
    in = pipe->in;
    in(&pipe->buf);
}

But I am getting the strange error:

pipe.c:107:5: note: expected 'struct pipe_buffer_s *' but argument is of type 'struct pipe_buffer_s *'

This makes no sense to me. As far as I can tell, I haven't goofed up and tried to use a struct of undefined length because I'm only using pointers here. I think I may have done something wrong with my typedef...

Changing the typedef to typedef void (*pipe_inf_t)(int); and calling in(5) works just fine however.

I get the same error if I move in and out into the pipe_buffer_s struct and call them from there so location doesn't seem to matter.

Any ideas?

@wildplasser I'm writing an OS in ANSI C. It's gcc with std=c89. — agregate
– agregate, Commented Feb 16, 2021 at 11:00
You'll need an opaque pointer before the pointer typedefs. Or change the order. — wildplasser
– wildplasser, Commented Feb 16, 2021 at 11:03
Is that the only warning or error you get? I get more than that. All the errors are fixed by moving the typedefs to be after struct pipe_buffer_s as the typedefs need that struct definition. — kaylum
– kaylum, Commented Feb 16, 2021 at 11:04
@kaylum Oh my gosh, you're absolutely right, that's what fixed it. — agregate
– agregate, Commented Feb 16, 2021 at 11:06

wildplasser · Accepted Answer · 2021-02-16 11:04:46Z

2

Add the definition of pipe_buffer_s before referring to it. This can be an incomplete type:

#include <stdlib.h>
#include <stdint.h>

struct pipe_buffer_s; // Incomplete definition

typedef void (*pipe_inf_t)(struct pipe_buffer_s *);
typedef void (*pipe_outf_t)(struct pipe_buffer_s *);

struct
pipe_buffer_s
{
    size_t cnt;      /* number of chars in buffer */
    size_t len;      /* length of buffer */
    uint8_t *mem;    /* buffer */
};

struct
pipe_s
{
    struct pipe_buffer_s buf;
    uint8_t state;
    pipe_inf_t in;   /* input call */
    pipe_outf_t out; /* output call */
};

// In my implementation, I have a function that attempts to call the function in:

void
pipe_receive(struct pipe_s *pipe)
{
    pipe_inf_t in;
    in = pipe->in;
    in(&pipe->buf);
}

answered Feb 16, 2021 at 11:04

wildplasser

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1 Comment

agregate Over a year ago

That is indeed the case. I may have had it well defined but I didn't have it defined quick enough... Thank you very much.

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