如何修复此NaN

Question

我试图做Java本地接口，这是使用gcc编译c文件和Java代码是

import java.util.Scanner;

class BMICalculator {

double weight, height;
native double BMIcalculate();

static {
    System.loadLibrary("Calculate");
}
public static void main(String args[]){
                      
            Scanner input = new Scanner(System.in);
            BMICalculator total = new BMICalculator();
                
            System.out.printf("Enter your weight : ");
            total.weight = input.nextDouble();
            System.out.printf("Enter your height : ");
            total.height = input.nextDouble();

            System.out.println("Your BMI is " + total.BMIcalculate());
                
        }

    }            

#include <jni.h>
#include <math.h>


JNIEXPORT jdouble JNICALL Java_BMICalculator_BMIcalculate(JNIEnv *env, jobject obj){
    
    jdouble total, weight1, height1 ;
    jfieldID fid1, fid2;
        
    jclass cls = (*env)->GetObjectClass(env,obj);
    fid1 = (*env)->GetFieldID(env,cls,"weight","D");
    fid2 = (*env)->GetFieldID(env,cls,"height","D");
    
    if((fid1 == NULL) || (fid2 == NULL)) return 0;
    
    
    weight1 = (*env)->GetDoubleField(env,obj,fid1);
    height1 = (*env)->GetDoubleField(env,obj,fid2);

    weight1 = (*env)->GetIntField(env,obj,fid1);
    height1 = (*env)->GetIntField(env,obj,fid2);
    
    
    
    height1 = height1 / 100;
    
    total = weight1 / ( height1 * height1 );    

        return total;
    
    
}

如何修复输出NaN

Answer 1

weight1 = (*env)->GetDoubleField(env,obj,fid1);
height1 = (*env)->GetDoubleField(env,obj,fid2);

weight1 = (*env)->GetIntField(env,obj,fid1);
height1 = (*env)->GetIntField(env,obj,fid2);

第二批线路在那里做什么？fid1和fid2是双字段的字段ID，因此应该如何读取它们。GetIntField生成未指定的结果。只需删除第二批行。

注意：如果这只是自学JNI，干得好。如果这是因为您认为它会“更快”，不，不会的，JVM在热点发现这类代码方面非常出色。这只是很难阅读，而且速度慢得多（JNI桥接绝对不是免费的）。