Structs mapped from C header need completeStruct pragma, otherwise sizeof doesn't work on those

[kaushalmodi]

Hello,

I recently came across one Nim object mapped to a C struct using nimterop that caused compilation failure only when I used sizeof to calculate the size of that struct.

Here's the relevant snippet from svdpi.h:

typedef struct t_vpi_vecval {
uint32_t aval;
uint32_t bval;
} s_vpi_vecval, *p_vpi_vecval;

typedef s_vpi_vecval svLogicVecVal;

Here's what Nimterop parses that to:

  t_vpi_vecval* {.bycopy, impsvdpiHdr, importc: "struct t_vpi_vecval".} = object
    aval*: uint32
    bval*: uint32

  s_vpi_vecval* {.importc, impsvdpiHdr.} = t_vpi_vecval
  p_vpi_vecval* {.importc, impsvdpiHdr.} = ptr t_vpi_vecval
  svLogicVecVal* {.importc, impsvdpiHdr.} = s_vpi_vecval

The code is functionally correct. But when I use sizeof on an object of type svLogicVecVal, I get:

9.struct_arrays/libdpi.nim(29, 24) Error: 'sizeof' requires '.importc' types to be '.completeStruct'

Looking around on Nim Forum, I found this post by @timotheecour and that helped!

I then put this in svdpi.nim, with the completeStruct pragma and everything worked:

cOverride:
  type
    t_vpi_vecval* {.bycopy, impsvdpiHdr, importc: "struct t_vpi_vecval", completeStruct.} = object
      aval*: uint32
      bval*: uint32
    s_vpi_vecval* {.importc, impsvdpiHdr, completeStruct.} = t_vpi_vecval
    svLogicVecVal* {.importc, impsvdpiHdr, completeStruct.} = s_vpi_vecval

cImport(cSearchPath("svdpi.h"), recurse = true, flags = "-f:ast2")

---

I don't completely understand why that pragma is needed in the first place.

Should nimterop be adding the completeStruct pragma automatically?

---

Reference code

---

Versions

• nim 1.4.6+
• nimterop 0.6.13