You can't name the inner struct. So here are the options: Say that you want this from C: struct Foo { struct Bar { int x; int y;

You can't name the inner struct. So here are the options: Say that you want this from C: struct Foo { struct Bar { int x; int y; } bar; }; struct Foo f; f.bar = (struct Bar) { .x = 123 }; The struct in C3: struct Foo { struct bar { int x; int y; } }; Foo f; It is correct that we don't get the inner type, but because C3 has inference for {} assignment can happen despite that: f.bar = { .x = 123 }; // Valid in C3 You can grab the type using typeof if you want, but interestingly there's also the possibility to use structural casts, which are valid in C3: struct HelperStruct { int x; int y; } HelperStruct test = (HelperStruct)f.bar; // structural cast But the normal way would be to create a named struct outside if you really need a named struct, e.g.: struct Bar { int x, y; } struct Foo { Bar bar; };