java C++ std::string to jstring 固定长度
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C++ std::string to jstring with a fixed length
提问by Eli Rising
I'm trying to turn a C++ std::string into a jstring and return it. This would be easy enough with
我正在尝试将 C++ std::string 转换为 jstring 并返回它。这很容易
JNIEnv*->NewStringUTF(stdString.c_str())
but the problem is that the string I'm converting has almost randomly interspersed null characters in it. This is a problem for the c_str(), but not the std::string. NewStringUTFwill only catch a portion of the full std::string. There is some hope in that the std::stringhas a length()function, which gets the full length, ignoring the problematic char* \0characters.
但问题是我正在转换的字符串中几乎随机散布着空字符。这是 的问题c_str()，但不是std::string。NewStringUTF只会捕获完整的一部分std::string。有一些希望std::string有一个length()函数，它获得全长，忽略有问题的 char*\0字符。
There's a separate function NewStringthat takes in a jchar* and a jsize*, so that looks promising, but I can't get the std::string converted properly to the jchar*. I tried making it a byte array, but I probably wasn't doing it right. I had further problems converting the int given by the length()into a jsize, which was required by the NewString call.
有一个单独的函数NewString接受 jchar* 和 jsize*，所以看起来很有希望，但我无法将 std::string 正确转换为 jchar*。我试着把它变成一个字节数组，但我可能做得不对。我在将 给出的 int 转换length()为 NewString 调用所需的 jsize 时遇到了进一步的问题。
I have done a bit of work with vector<char> byteArray(stdString.begin(), stdString.end()), but that didn't get me very far, probably because that is messing up what the original string is.
我已经用 做了一些工作vector<char> byteArray(stdString.begin(), stdString.end())，但这并没有让我走得很远，可能是因为这弄乱了原始字符串的内容。
Here is the basic starter function I have, which worked with strings without null chars:
这是我拥有的基本启动函数，它处理没有空字符的字符串：
jstring StringToJString(JNIEnv * env, const std::string & nativeString) {
return env->NewStringUTF(nativeString.c_str());
}
As a side note, this function is being used inside a JNI wrapper file for returning an object's std::string.
作为旁注，此函数在 JNI 包装器文件中使用，用于返回对象的std::string.
Thanks for any help or information sources!
感谢任何帮助或信息来源！
回答by Eli Rising
I made my own workaround solution taking RedAlert's advice.
我根据 RedAlert 的建议制定了自己的解决方案。
Java now expects a byte[] from the native call:
Java 现在需要来自本机调用的 byte[]：
private native byte[] toString(long thiz);
The toString method now calls this method inside it on a std::string:
toString 方法现在在其内部调用此方法std::string：
jbyteArray StringToJByteArray(JNIEnv * env, const std::string &nativeString) {
jbyteArray arr = env->NewByteArray(nativeString.length());
env->SetByteArrayRegion(arr,0,nativeString.length(),(jbyte*)nativeString.c_str());
return arr;
}
And the java level receives the data like this:
而java级别接收数据是这样的：
byte[] byteArray = toString(mNativeInstance);
String nativeString = "";
try {
nativeString = new String(byteArray, "UTF-8");
} catch (UnsupportedEncodingException e) {
Log.e(TAG, "Couldn't convert the jbyteArray to UTF-8");
e.printStackTrace();
}
