如何从
Java端(通过JNI)访问C头文件中定义的常量?
我有一个带有头文件c_header.h的C库:
// I'll try to get these values in java #define PBYTES 64 #define SBYTES 128 #define SGBYTES 128
然后我有这个java代码libbind_jni.java:
package libbind; public class libbind_jni { static{ try { System.load("libbind_jni.so"); } catch (UnsatisfiedLinkError e) { System.err.println("Native code library Failed to load.\n" + e); System.exit(1); } } public static native String[] pubm(String seed);
然后在libbind_jni.java上运行javah我生成JNI头文件jni_header.h:
#ifdef __cplusplus extern "C" { #endif /* * Class: libbind_libbind_jni * Method: pubm * Signature: (Ljava/lang/String;)[Ljava/lang/String; */ JNIEXPORT jobjectArray JNICALL Java_lib_f_1jni_pubm (JNIEnv *,jclass,jstring);
然后我为JNI库jni_source.c写了一个小C代码:
#include "jni_header.h" #include "c_header.h" #include <stdlib.h> JNIEXPORT jobjectArray JNICALL Java_libbind_libbind_1jni_pubm (JNIEnv *env,jclass cls,jstring jniSeed){ unsigned char vk[PBYTES]; unsigned char sk[SBYTES]; <whatever...> }
– 这里编译java库的库 – libbind.so
而JAVA源码j_source.java:
import libbind.libbind_jni; public class test { /* trying to access constants from library (libbind.so) */ System.out.println(libbind_jni.PBYTES); System.out.println(libbind_jni.SBYTES); System.out.println(libbind_jni.SGBYTES); } public static void main(String[] args) { test(); } $javac test.java test.java:5: cannot find symbol symbol : variable PBYTES location: class libbind.libbind_jni System.out.println(libbind_jni.PBYTES);
所以问题是:如何从Java访问C头文件中的这些定义/常量?
谢谢.
解决方法
简单的答案是,你做不到.您必须在Java中定义相同的值.
public static final int PBYTES = 64; public static final int SBYTES = 128; public static final int SGBYTES = 128;
或者,您可以定义一些返回这些值的本机方法.但是这样的宏不能从Java访问.
public static native int PBYTES(); public static native int SBYTES(); public static native int SGBYTES();