C++库在KMP项目中IOS调用示例

概述

本文档详细介绍如何在KMP项目中集成现有的C++库，通过分层架构实现iOS和Android平台的代码共享。以字符串相似度计算为例，展示完整的iOS调用流程。

整体架构图

iOS (Swift) → KMP自动生成胶水层 → C胶水层 → C++核心库

C++核心库实现

1. 头文件定义 (levenshtein.h)

#ifndef LEVENSHTEIN_H
#define LEVENSHTEIN_H

#include <string>

class StringProcessor {
public:
    StringProcessor(const std::string& baseStr);
    double calculateSimilarity(const std::string& target) const;
    
private:
    std::string baseString;
    int computeEditDistance(const std::string& a, const std::string& b) const;
};

#endif

2. 实现文件 (levenshtein.cpp)

#include "levenshtein.h"

StringProcessor::StringProcessor(const std::string& baseStr) : baseString(baseStr) {}

double StringProcessor::calculateSimilarity(const std::string& target) const {
    if (baseString.empty() && target.empty()) return 1.0;
    int maxLen = (baseString.length() > target.length()) ? baseString.length() : target.length();
    int distance = computeEditDistance(baseString, target);
    return 1.0 - (static_cast<double>(distance) / maxLen);
}

int StringProcessor::computeEditDistance(const std::string& a, const std::string& b) const {
    if (a == b) return 0;
    return (a.length() > b.length()) ? a.length() - b.length() : b.length() - a.length();
}

C胶水层开发

1. C接口声明 (string_glue.h)

#ifndef STRING_GLUE_H
#define STRING_GLUE_H

#ifdef __cplusplus
extern "C" {
#endif

typedef void* StringProcessorHandle;

StringProcessorHandle create_processor(const char* base);
double calc_similarity(StringProcessorHandle handle, const char* target);
void destroy_processor(StringProcessorHandle handle);

#ifdef __cplusplus
}
#endif

#endif

2. C++实现 (string_glue.cp)

#include "string_glue.h"
#include "levenshtein.h"

extern "C" {
    
    StringProcessorHandle create_processor(const char* base) {
        try {
            return new StringProcessor(std::string(base));
        } catch (...) {
            return nullptr;
        }
    }
    
    double calc_similarity(StringProcessorHandle handle, const char* target) {
        if (!handle || !target) return -1.0;
        
        StringProcessor* processor = static_cast<StringProcessor*>(handle);
        
        try {
            return processor->calculateSimilarity(std::string(target));
        } catch (...) {
            return -1.0;
        }
    }
    
    void destroy_processor(StringProcessorHandle handle) {
        if (handle) {
            delete static_cast<StringProcessor*>(handle);
        }
    }
}

KMP配置与封装

1. Gradle配置 (build.gradle.kts)

kotlin {
    iosX64()
    iosArm64()
    
    sourceSets {
        val iosMain by getting {
            dependencies {
                implementation(kotlin("stdlib"))
            }
        }
    }

    targets.withType<org.jetbrains.kotlin.gradle.plugin.mpp.KotlinNativeTarget> {
        binaries.withType<org.jetbrains.kotlin.gradle.plugin.mpp.Framework> {
            linkerOpts.add("-lstdc++")
        }
    }
}

2.Kotlin封装类 (StringProcessor.kt)

import kotlinx.cinterop.*
import platform.Foundation.*

import stringglue.* 

class NativeStringProcessor(private val base: String) : AutoCloseable {
    
    private val processorRef: CPointerVarOf<Any> = interpretCPointer(
        create_processor(base)?.ptr
    )!!

    fun calculateSimilarity(target: String): Double {
        return memScoped {
            val result = target.utf8CString { cString ->
                calc_similarity(processorRef.rawValue.toLong(), cString.ptr)
            }
            result
        }
    }

    override fun close() {
        destroy_processor(processorRef.rawValue.toLong())
    }
}

iOS Swift调用

import SharedKit
import UIKit

class ViewController: UIViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let processor = NativeStringProcessor(base: "HelloWorld")
        
        let similarity = processor.calculateSimilarity(target: "Hello KMP")
        
        print("相似度: $similarity)")
        
        // processor.close() // 手动释放资源
    }
}

项目结构

shared/
├── src/
│   ├── nativeInterop/
│   │   └── c/
│   │       ├── include/
│   │       │   ├── levenshtein.h
│   │       │   ├── levenshtein.cpp
│   │       │   ├── string_glue.h
│   │       │   └── string_glue.cpp
│   │       └── def/
│   │           └── stringglue.def
│   └── commonMain/
│       └── kotlin/
│           └── StringProcessor.kt