9.7 练习：C 库

译文 · 基于 Comprehensive Rust

原文链接: https://google.github.io/comprehensive-rust/unsafe-deep-dive/ffi/c-library-example.html

9.7 练习：C 库

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#ifndef TEXT_ANALYSIS_H
#define TEXT_ANALYSIS_H

#include <stddef.h>
#include <stdbool.h>

typedef struct TextAnalyst TextAnalyst;

typedef struct {
    const char* start;
    size_t length;
    size_t index;
} Token;

typedef enum {
    TA_OK = 0,
    TA_ERR_NULL_POINTER,
    TA_ERR_OUT_OF_MEMORY,
    TA_ERR_OTHER,
} TAError;

/* 返回 `false` 表示未找到 token。 */
typedef bool (*Tokenizer)(Token* token, void* extra_context);


typedef bool (*TokenCallback)(void* user_context, Token* token, void* result);

/* TextAnalyst 构造函数 */
TextAnalyst* ta_new(void);

/* TextAnalyst 析构函数 */
void ta_free(TextAnalyst* ta);

/* 重置状态以清除当前文档 */
void ta_reset(TextAnalyst* ta);

/* 使用自定义分词器（默认为空白符） */
void ta_set_tokenizer(TextAnalyst* ta, Tokenizer* func);

TAError ta_set_text(TextAnalyst* ta, const char* text, size_t len, bool make_copy);

/* 对每个 token 应用 `callback` */
size_t ta_foreach_token(const TextAnalyst* ta, const TokenCallback* callback, void* user_context);

/* 获取人类可读的错误信息 */
const char* ta_error_string(TAError error);

#endif /* TEXT_ANALYSIS_H */

C 库常用 void* 参数隐藏实现细节。

考虑这个自然语言处理库的头文件，它隐藏了 TextAnalyst 与 Analysis 类型。

在 Rust 中可用类似下面的类型来模拟：

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// Copyright 2026 Google LLC // SPDX-License-Identifier: Apache-2.0 #[repr(C)] pub struct TextAnalyst { _private: [u8; 0], }

练习：请学员为该库编写包装器。

建议解法

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// Copyright 2026 Google LLC // SPDX-License-Identifier: Apache-2.0 // ffi.rs use std::ffi::c_char; use std::os::raw::c_void; #[repr(C)] pub struct TextAnalyst { _private: [u8; 0], } #[repr(C)] #[derive(Debug, Clone, Copy)] pub struct Token { pub start: *const c_char, pub length: usize, pub index: usize, } #[repr(C)] #[derive(Debug, Clone, Copy, PartialEq, Eq)] pub enum TAError { Ok = 0, NullPointer = 1, OutOfMemory = 2, Other = 3, } pub type Tokenizer = Option< unsafe extern "C" fn(token: *mut Token, extra_context: *mut c_void) -> bool, >; pub type TokenCallback = Option< unsafe extern "C" fn( user_context: *mut c_void, token: *mut Token, result: *mut c_void, ) -> bool, >; unsafe extern "C" { pub fn ta_new() -> *mut TextAnalyst; pub fn ta_free(ta: *mut TextAnalyst); pub fn ta_reset(ta: *mut TextAnalyst); pub fn ta_set_tokenizer(ta: *mut TextAnalyst, func: *const Tokenizer); pub fn ta_set_text( ta: *mut TextAnalyst, text: *const c_char, len: usize, make_copy: bool, ) -> TAError; pub fn ta_foreach_token( ta: *const TextAnalyst, callback: *const TokenCallback, user_context: *mut c_void, ) -> usize; pub fn ta_error_string(error: TAError) -> *const c_char; }