JNI头文件生成与应用：为何标准C头文件不适用

#ifndef _BITMAP_H
#define _BITMAP_H 1

struct BITMAP
{
    char *buffer;   // buffer 
    int   ax;       // width
    int   ay;       // height
    int   size;     // buffer size
};
struct BITMAP *create(int ax, int ay);
void close( struct BITMAP *pbmp );
void drawLn( struct BITMAP *pbmp, int x1, int y1, int x2, int y2 );
void drawTxt(struct BITMAP *pbmp, char *szText, int x, int y );
void setPxl( struct BITMAP *pbmp, int x, int y );
#endif

// src/main/java/com/example/MyNativeLib.java
package com.example;

public class MyNativeLib {
    // 声明一个原生方法，用于创建BITMAP结构体
    public native long createNativeBitmap(int width, int height);

    // 声明一个原生方法，用于绘制线条
    public native void drawLine(long bitmapPtr, int x1, int y1, int x2, int y2);

    // 声明一个原生方法，用于关闭并释放BITMAP资源
    public native void closeBitmap(long bitmapPtr);

    // 静态代码块，用于加载本地库
    static {
        // "mynativelib" 是本地库的名称，例如在Linux上是libmynativelib.so
        System.loadLibrary("mynativelib");
    }

    public static void main(String[] args) {
        MyNativeLib lib = new MyNativeLib();
        long bitmapHandle = lib.createNativeBitmap(100, 50);
        if (bitmapHandle != 0) {
            System.out.println("Native bitmap created at handle: " + bitmapHandle);
            lib.drawLine(bitmapHandle, 0, 0, 99, 49);
            System.out.println("Line drawn.");
            lib.closeBitmap(bitmapHandle);
            System.out.println("Native bitmap closed.");
        } else {
            System.err.println("Failed to create native bitmap.");
        }
    }
}

# 假设当前位于项目根目录，Java源文件在 src/main/java
# 首先编译Java源文件
javac -d target/classes src/main/java/com/example/MyNativeLib.java

# 然后生成JNI头文件到指定的目录（例如当前目录的 'jni' 文件夹）
# 确保 target/classes 目录存在编译后的 .class 文件
javac -h jni -classpath target/classes src/main/java/com/example/MyNativeLib.java

/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class com_example_MyNativeLib */

#ifndef _Included_com_example_MyNativeLib
#define _Included_com_example_MyNativeLib
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     com_example_MyNativeLib
 * Method:    createNativeBitmap
 * Signature: (II)J
 */
JNIEXPORT jlong JNICALL Java_com_example_MyNativeLib_createNativeBitmap
  (JNIEnv *, jobject, jint, jint);

/*
 * Class:     com_example_MyNativeLib
 * Method:    drawLine
 * Signature: (JIIII)V
 */
JNIEXPORT void JNICALL Java_com_example_MyNativeLib_drawLine
  (JNIEnv *, jobject, jlong, jint, jint, jint, jint);

/*
 * Class:     com_example_MyNativeLib
 * Method:    closeBitmap
 * Signature: (J)V
 */
JNIEXPORT void JNICALL Java_com_example_MyNativeLib_closeBitmap
  (JNIEnv *, jobject, jlong);

#ifdef __cplusplus
}
#endif
#endif