构建工具

本节介绍在编译 crate 源代码之前运行的“构建时”工具或代码。按照惯例,构建时代码存放在 build.rs 文件,通常称为“构建脚本”。常见的用例包括:Rust 代码生成、绑定的 C/C++/asm 代码的编译。要获取更多信息,请阅读 Cargo(中文文档) 的构建脚本文档

静态编译并链接到绑定的 C 语言库

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To accommodate scenarios where additional C, C++, or assembly is required in a project, the cc crate offers a simple api for compiling bundled C/C++/asm code into static libraries (.a) that can be statically linked to by rustc.

The following example has some bundled C code (src/hello.c) that will be used from rust. Before compiling rust source code, the “build” file (build.rs) specified in Cargo.toml runs. Using the cc crate, a static library file will be produced (in this case, libhello.a, see compile docs) which can then be used from rust by declaring the external function signatures in an extern block.

Since the bundled C is very simple, only a single source file needs to be passed to cc::Build. For more complex build requirements, cc::Build offers a full suite of builder methods for specifying include paths and extra compiler flags.

Cargo.toml

[package]
...
build = "build.rs"

[build-dependencies]
cc = "1"

[dependencies]
error-chain = "0.11"

build.rs

fn main() {
    cc::Build::new()
        .file("src/hello.c")
        .compile("hello");   // outputs `libhello.a`
}

src/hello.c

#include <stdio.h>


void hello() {
    printf("Hello from C!\n");
}

void greet(const char* name) {
    printf("Hello, %s!\n", name);
}

src/main.rs

use error_chain::error_chain;
use std::ffi::CString;
use std::os::raw::c_char;

error_chain! {
    foreign_links {
        NulError(::std::ffi::NulError);
        Io(::std::io::Error);
    }
}
fn prompt(s: &str) -> Result<String> {
    use std::io::Write;
    print!("{}", s);
    std::io::stdout().flush()?;
    let mut input = String::new();
    std::io::stdin().read_line(&mut input)?;
    Ok(input.trim().to_string())
}

extern {
    fn hello();
    fn greet(name: *const c_char);
}

fn main() -> Result<()> {
    unsafe { hello() }
    let name = prompt("What's your name? ")?;
    let c_name = CString::new(name)?;
    unsafe { greet(c_name.as_ptr()) }
    Ok(())
}

静态编译并链接到绑定的 C++ 语言库

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Linking a bundled C++ library is very similar to linking a bundled C library. The two core differences when compiling and statically linking a bundled C++ library are specifying a C++ compiler via the builder method cpp(true) and preventing name mangling by the C++ compiler by adding the extern "C" section at the top of our C++ source file.

Cargo.toml

[package]
...
build = "build.rs"

[build-dependencies]
cc = "1"

build.rs

fn main() {
    cc::Build::new()
        .cpp(true)
        .file("src/foo.cpp")
        .compile("foo");   
}

src/foo.cpp

extern "C" {
    int multiply(int x, int y);
}

int multiply(int x, int y) {
    return x*y;
}

src/main.rs

extern {
    fn multiply(x : i32, y : i32) -> i32;
}

fn main(){
    unsafe {
        println!("{}", multiply(5,7));
    }   
}

编译 C 语言库时自定义设置

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It is simple to build bundled C code with custom defines using cc::Build::define. The method takes an Option value, so it is possible to create defines such as #define APP_NAME "foo" as well as #define WELCOME (pass None as the value for a value-less define). This example builds a bundled C file with dynamic defines set in build.rs and prints “Welcome to foo - version 1.0.2“ when run. Cargo sets some environment variables which may be useful for some custom defines.

Cargo.toml

[package]
...
version = "1.0.2"
build = "build.rs"

[build-dependencies]
cc = "1"

build.rs

fn main() {
    cc::Build::new()
        .define("APP_NAME", "\"foo\"")
        .define("VERSION", format!("\"{}\"", env!("CARGO_PKG_VERSION")).as_str())
        .define("WELCOME", None)
        .file("src/foo.c")
        .compile("foo");
}

src/foo.c

#include <stdio.h>

void print_app_info() {
#ifdef WELCOME
    printf("Welcome to ");
#endif
    printf("%s - version %s\n", APP_NAME, VERSION);
}

src/main.rs

extern {
    fn print_app_info();
}

fn main(){
    unsafe {
        print_app_info();
    }   
}