how to use "c-style flags enum" from c++ code?

Question

ef_vi_alloc_from_pd function from this c code accepts enum as last argument:

int ef_vi_alloc_from_pd(ef_vi* vi, ef_driver_handle vi_dh,
            struct ef_pd* pd, ef_driver_handle pd_dh,
            int evq_capacity, int rxq_capacity, int txq_capacity,
            ef_vi* evq_opt, ef_driver_handle evq_dh,
            enum ef_vi_flags flags)

In this c example we define flags as unsigned vi_flags and it works:

  unsigned vi_flags;
  vi_flags = EF_VI_FLAGS_DEFAULT;
  if( cfg_timestamping )
    vi_flags |= EF_VI_RX_TIMESTAMPS;
  TRY(ef_vi_alloc_from_pd(&res->vi, res->dh, &res->pd, res->dh,
                          -1, -1, 0, NULL, -1, vi_flags));

But in c++ it doesn't work, I have compile error when calling ef_vi_alloc_from_pd error: invalid conversion from ‘unsigned int’ to ‘ef_vi_flags’ [-fpermissive]

I've tried to define vi_flags as enum:

enum ef_vi_flags vi_flags;
vi_flags = EF_VI_FLAGS_DEFAULT;
vi_flags |= EF_VI_RX_TIMESTAMPS;

But this doesn't compile too, when I doing "|=" error: invalid conversion from ‘int’ to ‘ef_vi_flags’ [-fpermissive]

How to use ef_vi_alloc_from_pd from c++?

how to declare vi_flags and how to call ef_vi_alloc_from_pd?
how to "|=" vi_flags?
add any options to compiler?

use a cast when? when I modify flags or when I call function? how to declare vi_flags? — Oleg Vazhnev
– Oleg Vazhnev, Commented Sep 19, 2016 at 9:29

Jarod42 · Accepted Answer · 2016-09-19 09:30:04Z

2

You may do:

ef_vi_flags vi_flags = ef_vi_flags(EF_VI_FLAGS_DEFAULT | EF_VI_RX_TIMESTAMPS);

answered Sep 19, 2016 at 9:30

Jarod42

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6 Comments

Oleg Vazhnev Over a year ago

i have such compile error expected ‘;’ before ‘vi_flags’ ef_vi_flags vi_flags = ef_vi_flags(EF_VI_FLAGS_DEFAULT | EF_VI_RX_TIMESTAMPS);. tried to use enum ef_vi_flags vi_flags =... and compile error again

cannot convert ‘ef_vi_flags’ to ‘ef_vi*’ for argument ‘1’ to ‘ef_vi_flags ef_vi_flags(ef_vi*)’   enum ef_vi_flags vi_flags = ef_vi_flags(EF_VI_FLAGS_DEFAULT);

Jarod42 Over a year ago

Have you enum ef_vi_flags defined somewhere ?

Oleg Vazhnev Over a year ago

of course, for example enum ef_vi_flags vi_flags = EF_VI_FLAGS_DEFAULT; compiles just fine

Jarod42 Over a year ago

@javapowered: Does ef_vi_flags vi_flags = EF_VI_FLAGS_DEFAULT; compile for you ? which compiler do you use ?

Oleg Vazhnev Over a year ago

this doesn't compile error: expected ‘;’ before ‘vi_flags’ ef_vi_flags vi_flags = EF_VI_RX_TIMESTAMPS; i'm using gcc

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