Using C++ classes and methods in Rust.

[SmolPatches]

I have a header file like this,

#pragma once
#include <cstdint>
#include <fstream>
#include <vector>

#pragma pack(push,1)
struct TGAHeader {
    std::uint8_t  idlength = 0;
    std::uint8_t  colormaptype = 0;
    std::uint8_t  datatypecode = 0;
    std::uint16_t colormaporigin = 0;
    std::uint16_t colormaplength = 0;
    std::uint8_t  colormapdepth = 0;
    std::uint16_t x_origin = 0;
    std::uint16_t y_origin = 0;
    std::uint16_t width = 0;
    std::uint16_t height = 0;
    std::uint8_t  bitsperpixel = 0;
    std::uint8_t  imagedescriptor = 0;
};
#pragma pack(pop)

struct TGAColor {
    std::uint8_t bgra[4] = {0,0,0,0};
    std::uint8_t bytespp = 4;
    std::uint8_t& operator[](const int i) { return bgra[i]; }
};

struct TGAImage {
    enum Format { GRAYSCALE=1, RGB=3, RGBA=4 };

    TGAImage() = default;
    TGAImage(const int w, const int h, const int bpp);
    bool  read_tga_file(const std::string filename);
    bool write_tga_file(const std::string filename, const bool vflip=true, const bool rle=true) const;
    void flip_horizontally();
    void flip_vertically();
    TGAColor get(const int x, const int y) const;
    void set(const int x, const int y, const TGAColor &c);
    int width()  const;
    int height() const;
private:
    bool   load_rle_data(std::ifstream &in);
    bool unload_rle_data(std::ofstream &out) const;

    int w = 0;
    int h = 0;
    std::uint8_t bpp = 0;
    std::vector<std::uint8_t> data = {};
};

and I am trying to use it from within Rust. Build.rs

fn main() {
    // Tell cargo to look for shared libraries in the specified directory
    println!("cargo:rustc-link-search=./tga");

    // Tell cargo to tell rustc to link the system bzip2
    // shared library.
    println!("cargo:rustc-link-lib=tgaimage");

    // Tell cargo to invalidate the built crate whenever the wrapper changes
    println!("cargo:rerun-if-changed=tgaimage.h");

    cxx_build::bridge("src/main.rs")  // returns a cc::Build
        .file("tga/tgaimage.cpp")
        .flag_if_supported("-std=c++20")
        .flag_if_supported("-fno-inline-functions")
        .include("tga")
        .compile("tgaimage");
}

With a rust bridge like in src/main.rs as follows,

use cxx::let_cxx_string;
mod tgaimage {
    #[cxx::bridge]
    pub mod ffi {
        unsafe extern "C++" {
            include!("tgaimage.h");
            type TGAImage;
            type TGAHeader;
            type TGAColor;
            pub fn read_tga_file(self:&TGAImage,filename:&CxxString) -> bool;
        }
    }
}
use tgaimage::ffi::*;
pub(crate) fn main() {
    let x: tgaimage::ffi::TGAImage;
}

When I run cargo b or cargo r The output I get when building is below,

warning: /Users/r3b/Documents/Projects/software_renderer/target/debug/build/software_renderer-9a5add0671fa0bbb/out/cxxbridge/sources/software_renderer/src/main.rs.cc:10:22: error: cannot initialize a variable of type 'bool (TGAImage::*)(const ::std::string &) const' with an rvalue of type 'bool (TGAImage::*)(const std::string)': type mismatch at 1st parameter ('const ::std::string &' (aka 'const basic_string<char, char_traits<char>, allocator<char>> &') vs 'const std::string' (aka 'const basic_string<char, char_traits<char>, allocator<char>>'))
warning:   bool (::TGAImage::*read_tga_file$)(::std::string const &) const = &::TGAImage::read_tga_file;
warning:                      ^                                              ~~~~~~~~~~~~~~~~~~~~~~~~~~
warning: 1 error generated.

error: failed to run custom build command for `software_renderer v0.1.0 (/Users/r3b/Documents/Projects/software_renderer)`

Caused by:
  process didn't exit successfully: `/Users/r3b/Documents/Projects/software_renderer/target/debug/build/software_renderer-5e0b03cc1cb43eb2/build-script-build` (exit status: 1)

What is the proper way to build a bridge to use a cstring in rust? Am I using CxxString incorrectly?

[metasim]

I have the same question. Any luck @SmolPatches?

[dtolnay]

Sorry that no one was able to provide guidance here. If this is still an issue, you could try taking this question to any of the resources shown in https://www.rust-lang.org/community.