Question

有没有办法获得configuration flag的价值？例如，我希望将target_os的值设为str / String，而不使用以下if-else-if链：

if cfg!(target_os = "windows") {
    "windows"
} else if cfg!(target_os = "linux") {
    "linux"
// ...
} else {
    "unknown"
}

Answer 1

没有。你可以通过欺骗货物告诉你，获得一些。如果您将以下内容放入build script：

use std::env;

fn main() {
    for (key, value) in env::vars() {
        if key.starts_with("CARGO_CFG_") {
            println!("{}: {:?}", key, value);
        }
    }
    panic!("stop and dump stdout");
}

...它将显示Cargo知道的cfg标志。 panic!只是让货物实际显示输出而不是隐藏输出的简单方法。作为参考，它产生的输出如下所示：

   Compiling dump-cfg v0.1.0 (file:///F:/Programming/Rust/sandbox/cargo-test/dump-cfg)
error: failed to run custom build command for `dump-cfg v0.1.0 (file:///F:/Programming/Rust/sandbox/cargo-test/dump-cfg)`
process didn't exit successfully: `F:\Programming\Rust\sandbox\cargo-test\dump-cfg\target\debug\build\dump-cfg-8b04f9ac3818f82a\build-script-build` (exit code: 101)
--- stdout
CARGO_CFG_TARGET_POINTER_WIDTH: "64"
CARGO_CFG_TARGET_ENV: "msvc"
CARGO_CFG_TARGET_OS: "windows"
CARGO_CFG_TARGET_ENDIAN: "little"
CARGO_CFG_TARGET_FAMILY: "windows"
CARGO_CFG_TARGET_ARCH: "x86_64"
CARGO_CFG_TARGET_HAS_ATOMIC: "16,32,64,8,ptr"
CARGO_CFG_TARGET_FEATURE: "sse,sse2"
CARGO_CFG_WINDOWS: ""
CARGO_CFG_TARGET_VENDOR: "pc"
CARGO_CFG_DEBUG_ASSERTIONS: ""

--- stderr
thread 'main' panicked at 'stop', build.rs:9
note: Run with `RUST_BACKTRACE=1` for a backtrace.

您可以从此列表中提取您感兴趣的值，并将它们转储到生成的源文件中，然后可以将其导入（使用#[path]或include!）到包的源代码中。

Answer 2

特别是对于target_os，以及仅target_family和target_arch，在std::env::consts::{OS, FAMILY, ARCH}中有相应的&str常量。

如何获取配置标志的值？

2 个答案: