# How to wrap C++ function writing to FILE\*?
**URL:** https://discourse.julialang.org/t/how-to-wrap-c-function-writing-to-file/122945
**Category:** General Usage
**Tags:** question, cxxwrap
**Created:** [November 22, 2024, 9:52am UTC](https://discourse.julialang.org/t/how-to-wrap-c-function-writing-to-file/122945 "2024-11-22T09:52:18Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@Vasily\_Pisarev](https://discourse.julialang.org/u/Vasily_Pisarev)
#### Post date: [November 22, 2024, 9:52am UTC](https://discourse.julialang.org/t/how-to-wrap-c-function-writing-to-file/122945/1 "2024-11-22T09:52:18Z")
I want to wrap a C++ function writing to a file stream to be able to print to a file or to `stdout` (eventually I’d like to try if `redirect_stdout` would work to make it print to a custom buffer). However, CxxWrap does not want to export it saying there is no factory for the IO\_FILE type. As far as I understand, such functions are supposed to take `Ptr{Libc.FILE}` from Julia. Is it possible to do that using CxxWrap?
For the reference, the C++ library in question is Voro++. It has some output functions that use protected and private class members internally, so that I cannot just port the implementation to Julia without patching the original library.
---
### Author:  [@Vasily\_Pisarev](https://discourse.julialang.org/u/Vasily_Pisarev)
#### Post date: [November 22, 2024, 9:11pm UTC](https://discourse.julialang.org/t/how-to-wrap-c-function-writing-to-file/122945/2 "2024-11-22T21:11:53Z")
Okay, I think I have found out a way to do that.
Instead of adding the needed method automatically via CxxWrap, I added a C wrapper function like the following:
```cpp
extern "C" {
void write_data(Object* obj, FILE* fp)
{
obj->write_data(fp);
}
}
```
And from Julia, I use `ccall` directly:
```julia
function write_data(io::IOStream, obj::CxxObject)
file = Libc.FILE(io)
ccall(
(:write_data, "libmywrapper"),
Cvoid,
(Ptr{Cvoid}, Ptr{Libc.FILE}),
obj.cpp_object, file,
)
close(file)
end
```