# An experimental Julia library: copyout csv from postgresql using rust and Clang.jl
**URL:** https://discourse.julialang.org/t/an-experimental-julia-library-copyout-csv-from-postgresql-using-rust-and-clang-jl/121100
**Category:** New to Julia
**Created:** [October 9, 2024, 9:57am UTC](https://discourse.julialang.org/t/an-experimental-julia-library-copyout-csv-from-postgresql-using-rust-and-clang-jl/121100 "2024-10-09T09:57:53Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@bluebug](https://discourse.julialang.org/u/bluebug)
#### Post date: [October 9, 2024, 9:57am UTC](https://discourse.julialang.org/t/an-experimental-julia-library-copyout-csv-from-postgresql-using-rust-and-clang-jl/121100/1 "2024-10-09T09:57:54Z")
copyout csv from postgresql, using rust postgres/cbindgen and Clang.jl to interop rust and julia together, without jirs.
Any suggestions for sharing complex data structures from Rust to Julia? like:
```rust
#[repr(C)]
pub enum DTypes {
I8 = 0,
I32 = 1,
I64 = 2,
F32 = 3,
F64 = 4,
Str = 5,
}
#[repr(C)]
pub struct DFrame {
pub width: u32,
pub height: u32,
pub fields: *mut *const u8, // field names
pub types: *mut DTypes, // field types
pub values: *mut *const c_void, // field values
}
```
### Purpose:
Use the rust postgres library to generate a postgresql client that can be quickly imported, and provide a copyout method to quickly obtain csv results.
### Prerequisites:
1. Rust environment
2. Julia environment with Clang.jl
3. Postgresql database
4. Modify the database link and test code in build.jl
### Compile method:
using global julia env
1. build step by step
```julia
include("build.jl")
build_rs()
build_jl()
test()
```
1. or build once
```cmd
julia build.jl
```
### howto:
Refer to the test code in build.jl
### changelog:
- 2024-10-09 v0.1.1:
- 2024-10-03 v0.1.0: initial version
[https://github.com/bluebug/libpq\_rsjl](https://source)
---
### Author:  [@bluebug](https://discourse.julialang.org/u/bluebug)
#### Post date: [October 10, 2024, 3:19pm UTC](https://discourse.julialang.org/t/an-experimental-julia-library-copyout-csv-from-postgresql-using-rust-and-clang-jl/121100/2 "2024-10-10T15:19:16Z")
- 2024-10-10 v0.2.0:
- add pq\_query\_native(rs)/pq\_query(jl) function to get dframe from postgresql
- add pq\_free\_dframe(rs) function to release dframe, but not sure if the rust code releases the memory correctly💣
- add test code for dframe in build.jl
- call unsafe\_string only when call copyout.body
help need:
how to view `Cstring` without copy? using `unsafe_string` causing copy.
```julia
unsafe_string(s:Cstring)
```
---
### Author:  [@mrufsvold](https://discourse.julialang.org/u/mrufsvold)
#### Post date: [October 10, 2024, 6:08pm UTC](https://discourse.julialang.org/t/an-experimental-julia-library-copyout-csv-from-postgresql-using-rust-and-clang-jl/121100/3 "2024-10-10T18:08:00Z")
I think you can use VectorStrings.jl for that!
---
### Author:  [@bluebug](https://discourse.julialang.org/u/bluebug)
#### Post date: [October 11, 2024, 7:17am UTC](https://discourse.julialang.org/t/an-experimental-julia-library-copyout-csv-from-postgresql-using-rust-and-clang-jl/121100/4 "2024-10-11T07:17:11Z")
Thanks, according to your suggestion, I found the library StringViews.jl, and now I can view CString without copying.
```julia
using StringViews
Base.length(cs::Cstring) = ccall(:strlen, Cint, (Cstring,), cs)
CStringView(cs::Cstring) = StringView(unsafe_wrap(Array, Ptr{UInt8}(cs), length(cs)))
Base.write(io::IO, cs::Cstring) = write(io, CStringView(cs))
Base.print(io::IO, cs::Cstring) = (write(io, CStringView(cs)); nothing)
Base.show(io::IO, cs::Cstring) = (write(io, CStringView(cs)); nothing)
Base.length(cs::Ptr{UInt8}) = ccall(:strlen, Cint, (Ptr{UInt8},), cs)
CStringView(cs::Ptr{UInt8}) = StringView(unsafe_wrap(Array, cs, length(cs)))
Base.write(io::IO, cs::Ptr{UInt8}) = write(io, CStringView(cs))
Base.print(io::IO, cs::Ptr{UInt8}) = (write(io, CStringView(cs)); nothing)
Base.show(io::IO, cs::Ptr{UInt8}) = (write(io, CStringView(cs)); nothing)
export CStringView
```