Comment by jibal

According to https://www.nokia.com/bell-labs/about/dennis-m-ritchie/chist..., which is authoritative:

> During 1973-1980, the language grew a bit: the type structure gained unsigned, long, union, and enumeration types, and structures became nearly first-class objects (lacking only a notation for literals).

And

> By 1982 it was clear that C needed formal standardization. The best approximation to a standard, the first edition of K&R, no longer described the language in actual use; in particular, it mentioned neither the void or enum types. While it foreshadowed the newer approach to structures, only after it was published did the language support assigning them, passing them to and from functions, and associating the names of members firmly with the structure or union containing them. Although compilers distributed by AT&T incorporated these changes, and most of the purveyors of compilers not based on pcc quickly picked up them up, there remained no complete, authoritative description of the language.

So passing structs entered the language before C89, and possibly was available in some compilers by 1979. I was very active in C during this period and was a member of X3J11 (I happen to be the first person ever to vote to standardize C, due to alphabetical order), but unfortunately I'm not able to pin down the timing from my own memory.

P.S. Page of 121 of K&R C, first edition, says "The essential rules are that the only operations that you can perform on a structure are take its address with c, and access one of its members. This implies that structures may not be assigned to or copied as a unit, and that they cannot be passed to or returned from functions. (These restrictions will be removed in forthcoming versions.)"

So they were already envisioning passing structs to functions in 1978.