jni jnienv GetStringUTFLength example c c++ java

GetStringUTFLength

jsize GetStringUTFLength(JNIEnv *env, jstring string);

Returns the length in bytes of the modified UTF-8 representation of a string.

LINKAGE:

Index 168 in the JNIEnv interface function table.

PARAMETERS of GetStringUTFLength

env: the JNI interface pointer.

string: a Java string object.

RETURNS of GetStringUTFLength

Returns the UTF-8 length of the string.

Example of GetStringUTFLength

jclass cls = env->GetObjectClass(obj);

// First get the class object
jmethodID mid = env->GetMethodID(cls, "getClass", "()Ljava/lang/Class;");
jobject clsObj = env->CallObjectMethod(obj, mid);

// Now get the class object's class descriptor
cls = env->GetObjectClass(clsObj);

// Find the getName() method on the class object
mid = env->GetMethodID(cls, "getName", "()Ljava/lang/String;");

// Call the getName() to get a jstring object back
jstring strObj = (jstring)env->CallObjectMethod(clsObj, mid);

// Now get the c string from the java jstring object
const char* str = env->GetStringUTFChars(strObj, NULL);

// Print the class name
printf("\nCalling class is: %s\n", str);

// Release the memory pinned char array
env->ReleaseStringUTFChars(strObj, str);

Note that I haven't taken any actions to check for errors. This is just a small code snippet describing how it could be done.

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Alternatively you could do this instead of using the GetStringUTFChars/ReleaseStringUTFChars:

// Make sure that the buffer is large enough
char str[128];
jint strlen = env->GetStringUTFLength(strObj);
env->GetStringUTFRegion(strObj, 0, strlen, str);
printf("\nCalling class is: %s\n", str);