无法使用bincode立即解码写入文件的对象

Question

当我尝试运行测试时,我收到此异常:

thread 'persistent_log::doc::test::test_sync' panicked at 'called `Result::unwrap()` on an `Err` value: IoError(Error { repr: Os { code: 9, message: "Bad file descriptor" } })', ../src/libcore/result.rs:783

术语:

#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, PartialOrd, Ord,RustcEncodable,RustcDecodable)]
pub struct Term(u64);

测试:

fn create() {
    File::create(&"term");
}

#[test]
fn test_sync() {
    create();

    let mut f = File::open(&"term").unwrap();

    let term = Term(10);

    encode_into(&term, &mut f, SizeLimit::Infinite).unwrap();

    let decoded_term: Term = decode_from(&mut f, SizeLimit::Infinite).unwrap();

    assert_eq!(decoded_term, term);
}

我想将对象term写入文件,然后将其读入.

Answer 1

File::open 以只读模式打开文件,因此写入文件将失败.

要打开具有读写访问权限的文件,必须使用OpenOptions.

use std::fs::OpenOptions;

let file = OpenOptions::new()
            .read(true)
            .write(true)
            .create(true)
            .open("term");

很好,但现在我得到一个新的例外:

thread 'persistent_log::doc::test::test_sync' panicked at 'called Result::unwrap() on an Err value: IoError(Error { repr: Custom(Custom { kind: UnexpectedEof, error: StringError("failed to fill whole buffer") }) })', ../src/libcore/result.rs:783

在将字节写入文件后,文件的光标将位于文件的末尾.您尝试从文件中读取之前,你必须设法回到文件的开始,否则你会得到这个错误.

file.seek(SeekFrom::Start(0));