JNA（十五）Double指针与数组

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本文介绍了如何在C语言和Java中通过JNA库操作动态链接库，包括双精度浮点数指针的设置、获取和清理，以及double数组的创建、读取和释放。特别强调了使用指针引用和内存偏移进行数组操作的方法。

文章目录

@[TOC](文章目录)

前言
操作
1.C语言代码
2.java代码
3.查看输出

总结

前言

关于环境和dll的生成，不懂的同学可以去查看JNA（一）与JNA（二）的内容
double数组的操作漏掉了，现补上

操作

1.C语言代码

头文件（library.h）

#ifndef CDYNAMICDEMO_LIBRARY_H
#define CDYNAMICDEMO_LIBRARY_H

#include <string.h>
#include <stdlib.h>

// double指针
void setDouble(const double *value);

double *getDouble();

void cleanDouble(double *value);

//double数组
double setDoubleArr(const double *arr, int num);

void getDoubleArr(double **arr, int *num);

void cleanDoubleArr(double *arr);

#endif //CDYNAMICDEMO_LIBRARY_H

代码文件（library.c）

#include "library.h"
#include <stdio.h>
void setDouble(const double *value) {
    printf("\nthe double value is: %f", *value);
}

double *getDouble() {
    double *value = malloc(sizeof(double));
    *value = 2.71828;
    return value;
}

void cleanDouble(double *value) {
    free(value);
}

double setDoubleArr(const double *arr, int num) {
    int j = 0;
    double total = 0;
    for (; j < num; j++) {
        total += arr[j];
    }
    return total;
}

void getDoubleArr(double **arr, int *num) {
    int i = 0;
    *num = 10;
    *arr = malloc(sizeof(double) * 10);
    memset(*arr, 0, sizeof(double) * 10);
    for (; i < *num; i++) {
        (*arr)[i] = (10 + i) / 100.0;
    }
}

void cleanDoubleArr(double *arr) {
    free(arr);
}

2.java代码

package com.dynamic.demo.base;

import com.sun.jna.*;
import com.sun.jna.ptr.DoubleByReference;
import com.sun.jna.ptr.IntByReference;
import com.sun.jna.ptr.PointerByReference;

public interface DoublePointAndArrayLibrary extends Library {
    DoublePointAndArrayLibrary INTANCE = Native.load(Platform.isWindows() ? "libCDynamicDemo" : "", DoublePointAndArrayLibrary.class);

    void setDouble(DoubleByReference reference);

    DoubleByReference getDouble();

    void cleanDouble(Pointer value);

    // double数组
    double setDoubleArr(Pointer arr, int num);

    void getDoubleArr(PointerByReference pointerByReference, IntByReference reference);

    void cleanDoubleArr(Pointer arr);

    public static void main(String[] args) {
        DoubleByReference reference = new DoubleByReference(3.1415);
        DoublePointAndArrayLibrary.INTANCE.setDouble(reference);

        DoubleByReference aDouble = DoublePointAndArrayLibrary.INTANCE.getDouble();
        System.out.println("获取double: " + aDouble.getValue());

        DoublePointAndArrayLibrary.INTANCE.cleanDouble(aDouble.getPointer());


        // 设置double数组
        int num = 5;
        int nativeSize = Native.getNativeSize(double.class);
        Pointer pointer = new Memory(num * nativeSize);
        for (int i = 0; i < num; i++) {
            pointer.setDouble(i * nativeSize, (10.1 + i) / 3.0);
        }
        double value = DoublePointAndArrayLibrary.INTANCE.setDoubleArr(pointer, num);
        System.out.println(value);

        // 获取double数组, PointerByReference是指针的指针
        PointerByReference arrReference = new PointerByReference();
        IntByReference intByReference = new IntByReference();
        DoublePointAndArrayLibrary.INTANCE.getDoubleArr(arrReference, intByReference);
        int len = intByReference.getValue();
        System.out.println("数组元素个数: " + len);
        if (intByReference.getValue() > 0) {
            Pointer pointer1 = arrReference.getValue();
            double total = 0;
            for (int i = 0; i < len; i++) {
                double val = pointer1.getDouble(i * nativeSize);
                total += val;
            }
            System.out.println("double数组的总和: " + total);

            DoublePointAndArrayLibrary.INTANCE.cleanDoubleArr(pointer1);
        }
    }
}