Coping with C pointers to functions

[russel]

Playing with libdvbv5 still: I am having a problem with function pointers. In the C code a function is declared:

dvb_v5_descriptors* dvb_scan_transponder (
    dvb_v5_fe_parms* parms,
    dvb_entry* entry,
    int dmx_fd,
    int function () check_frontend,
    void* args,
    uint other_nit,
    uint timeout_multiply);

however, the check_frontend project has to be a function with signature:

int function (void* args, dvb_v5_fe_parms* parms)

there is a type check_frontend_t but the declaration of dvb_scan_transponder seems not to use it, which is very C obviously. It means though I end up with the error:

../../Repositories/Git/Masters/DVBTune/source/libdvbv5.d(139): Error: function dvb_scan.dvb_scan_transponder (dvb_v5_fe_parms* parms, dvb_entry* entry, int dmx_fd, extern (C) int function() check_frontend, void* args, uint other_nit, uint timeout_multiply) is not callable using argument types (dvb_v5_fe_parms*, dvb_entry*, int, extern (C) int function(void* args, dvb_v5_fe_parms* parms), void*, uint, uint)

For which D seems to offer no solution since cast(extern (C) int function()) is not a valid cast.

Obviously the hack of the moment is to manually change the declaration, but I suspect the solution is to correct the upstream source. I guess I am flagging this in case someone knows a workaround.

[jacob-carlborg]

Could you send please include the an example of how the declaration of the function looks like in the header file.

[russel]

The C header file declaration of the function is:

struct dvb_v5_descriptors *dvb_scan_transponder(struct dvb_v5_fe_parms *parms,
                                                struct dvb_entry *entry,
                                                int dmx_fd,
                                                check_frontend_t *check_frontend,
                                                void *args,
                                                unsigned other_nit,
                                                unsigned timeout_multiply);

so I am now wondering why the post dstep declaration is:

dvb_v5_descriptors* dvb_scan_transponder (
    dvb_v5_fe_parms* parms,
    dvb_entry* entry,
    int dmx_fd,
    int function () check_frontend,
    void* args,
    uint other_nit,
    uint timeout_multiply);

[jacob-carlborg]

Can you include the exact declaration of check_frontend_t as well?

[russel]

typedef int (check_frontend_t)(void *args, struct dvb_v5_fe_parms *parms);