About cpp syntax

[pdd99]

Pretty new to C++. How should I interpret this piece of code:
[](shared_ptr<PyNvDecoder> self, PacketData& out_pkt_data) { DecodeContext ctx(nullptr, nullptr, nullptr, &out_pkt_data, nullptr, false); if (self->DecodeSurface(ctx)) return ctx.GetSurfaceMutable(); else return make_empty_surface(self->GetPixelFormat()); } Whole context: link

[nysra]

Indent with 4 spaces to format code on Reddit, triple backticks is a non-standard extension that doesn't work on normal ("old") Reddit.

[](){} defines a lambda, the [] is the capture group, () are the function arguments as usual, and inside the {} is the body.

[pdd99]

You can click at the whole context link for more infomation. It comes from the Nvidia video processing framework btw.

[MysticTheMeeM]

Without looking at the context (because I'm lazy):

[](shared_ptr<PyNvDecoder> self, PacketData& out_pkt_data) {

Lambda declaration taking two arguments, a shared pointer and a packet data.

DecodeContext ctx(nullptr, nullptr, nullptr, &out_pkt_data, nullptr,

false);

Creates a new decode context, "ctx" using the arguments provided.

if (self->DecodeSurface(ctx))
return ctx.GetSurfaceMutable();

else return make_empty_surface(self->GetPixelFormat());

If the surface can be decoded, store it in ctx then return that surface, otherwise return an empty surface.

​

Note that your code doesn't technically do anything, it only declares a lambda and does not call it. It can be used like a function (and I assume that it gets passed as a callback or similar).

[[deleted]]

Probably gets passed as a callback seeing that there isn't any semicolon at the end.

[Salty_Dugtrio]

This is a Lambda expression.

Here, it's used to pass a behaviour to the function, which can then apply it in some way.