JNI和C++中的String相互转换

待我称王封你为后i 2022-06-17 21:10 245阅读 0赞

原文：[http://blog.csdn.net/uper945/article/details/1935706][http_blog.csdn.net_uper945_article_details_1935706]

JNI和C++中的String相互转换  
Uper

目前仍在继续先前的工作，这两天一直在折腾jstring 和char\* 之间是如何转换的。在网上找了些例子和张孝祥jni的视频，现把自己成功运行例子贴出来。  
  
//jstring to char\*  
char\* jstringTostring(JNIEnv\* env, jstring jstr)  
\{  
       char\* rtn = NULL;  
       jclass clsstring = env->FindClass("java/lang/String");  
       jstring strencode = env->NewStringUTF("utf-8");  
       jmethodID mid = env->GetMethodID(clsstring, "getBytes", "(Ljava/lang/String;)\[B");  
       jbyteArray barr= (jbyteArray)env->CallObjectMethod(jstr, mid, strencode);  
       jsize alen = env->GetArrayLength(barr);  
       jbyte\* ba = env->GetByteArrayElements(barr, JNI\_FALSE);  
       if (alen > 0)  
       \{  
                 rtn = (char\*)malloc(alen + 1);  
                 memcpy(rtn, ba, alen);  
                 rtn\[alen\] = 0;  
       \}  
       env->ReleaseByteArrayElements(barr, ba, 0);  
       return rtn;  
\}  
  
//char\* to jstring  
jstring stoJstring(JNIEnv\* env, const char\* pat)  
\{  
       jclass strClass = env->FindClass("Ljava/lang/String;");  
       jmethodID ctorID = env->GetMethodID(strClass, "<init>", "(\[BLjava/lang/String;)V");  
       jbyteArray bytes = env->NewByteArray(strlen(pat));  
       env->SetByteArrayRegion(bytes, 0, strlen(pat), (jbyte\*)pat);  
       jstring encoding = env->NewStringUTF("utf-8");  
       return (jstring)env->NewObject(strClass, ctorID, bytes, encoding);  
\}  
  
//invoke function  
JNIEXPORT jstring JNICALL Java\_test\_cs\_web\_SWIFTAlianceCASmfTest\_strcal  
  (JNIEnv \*env, jclass obj, jstring jstr1, jstring jstr2)  
\{  
    jbyteArray bytes = 0;  
    jthrowable exc;  
    char \*pszResult = NULL;      
    char \*pszSTR1 = NULL;  
    char \*pszSTR2 = NULL;  
      
    pszSTR1 = jstringTostring(env, jstr1);  
    pszSTR2 = jstringTostring(env, jstr2);  
  
    int nlen = sizeof(char)\*(strlen(pszSTR1)+strlen(pszSTR2));  
    pszResult = (char\*)malloc(nlen);  
    strcpy(pszResult, pszSTR1);  
    strcat(pszResult, pszSTR2);  
  
    jstring jstrRe = stoJstring(env, pszResult);  
    free(pszSTR1);  
    free(pszSTR2);  
    free(pszResult);  
    return(jstrRe);  
\}   
  
Note: 函数中间有一些签名的定义，不是很好理解。细节请参考sun的jni文档介绍or command javap

[http_blog.csdn.net_uper945_article_details_1935706]: http://blog.csdn.net/uper945/article/details/1935706