wise lake
I'm writing a zig app to list V4L2 device capabilities
They are defined in /usr/include/linux/videodev2.h in field capabilities of struct v4l2_capability where each bit represents a capability. So essentially a bit flag.
How does it translate to zig? Should I use packed struct ? If so could you show an example of how to display capabilitties from an int?
brave forge
Are you writing bindings? If not, you can use them same way as in C
If you want to represent the bitlflags as packed struct for nicer interface then that's possible indeed.
const Capabilities = packed struct (u32) {
video_capture: bool = false,
video_output: bool = false,
video_overlay: bool = false,
vbi_capture: bool = false,
vbi_output: bool = false,
// and so on ...
};
you can @bitCast this struct into/from u32 then
wise lake
awesome. Thanks!
it looks like there are 29 possibilities. I had to do something like:
const Capabilities = packed struct(u32) {
//...
DEVICE_CAPS: bool,
RESERVED1: bool,
RESERVED2: bool,
RESERVED3: bool,
is there another way?
Even something like:
const Capabilities = packed struct(u32) {
//...
DEVICE_CAPS: bool,
RESERVED: u3,
}
seems a bit awkward
undone sluice
Maybe @Vector of bools will work?
brave forge
you need to pad rest of the struct
RESERVED: u3 is fine
or I usually do _: u3
also the zig way is to use lowercase field names
wise lake
Actually it looks like this:
const Capabilities = packed struct(u32) {
// .. some caps
RESERVED1: bool,
// .. more caps
RESERVED1: bool,
}
so I cannot use the _: bool syntax, can I?
brave forge
nah, have to give unique name sadly
wise lake
is there a generic way to print the fields with true value? Something like an instrospection api?
brave forge
pub fn format(self: @This(), comptime _: []const u8, _: std.fmt.FormatOptions, writer: anytype) !void {
inline for (std.meta.fields(@This()) |field| {
try writer.print("{s}: {}", .{field.name, @field(self, field.name)};
}
}
};
something like that, untested (prints all fields and their variable)
wise lake
I got something working:
fn fmt(comptime T: type, value: T, writer: anytype) !void {
inline for (std.meta.fields(T)) |field| {
if (@field(value, field.name)) {
try writer.print("{s}, ", .{field.name});
}
}
}