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      1 /*
      2  * Copyright (C) 2010 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 #ifndef SCOPED_UTF_CHARS_H_
     18 #define SCOPED_UTF_CHARS_H_
     19 
     20 #include <string.h>
     21 
     22 #include "jni.h"
     23 #include "nativehelper_utils.h"
     24 
     25 // A smart pointer that provides read-only access to a Java string's UTF chars.
     26 // Unlike GetStringUTFChars, we throw NullPointerException rather than abort if
     27 // passed a null jstring, and c_str will return nullptr.
     28 // This makes the correct idiom very simple:
     29 //
     30 //   ScopedUtfChars name(env, java_name);
     31 //   if (name.c_str() == nullptr) {
     32 //     return nullptr;
     33 //   }
     34 class ScopedUtfChars {
     35  public:
     36   ScopedUtfChars(JNIEnv* env, jstring s) : env_(env), string_(s) {
     37     if (s == nullptr) {
     38       utf_chars_ = nullptr;
     39       jniThrowNullPointerException(env, nullptr);
     40     } else {
     41       utf_chars_ = env->GetStringUTFChars(s, nullptr);
     42     }
     43   }
     44 
     45   ScopedUtfChars(ScopedUtfChars&& rhs) :
     46       env_(rhs.env_), string_(rhs.string_), utf_chars_(rhs.utf_chars_) {
     47     rhs.env_ = nullptr;
     48     rhs.string_ = nullptr;
     49     rhs.utf_chars_ = nullptr;
     50   }
     51 
     52   ~ScopedUtfChars() {
     53     if (utf_chars_) {
     54       env_->ReleaseStringUTFChars(string_, utf_chars_);
     55     }
     56   }
     57 
     58   ScopedUtfChars& operator=(ScopedUtfChars&& rhs) {
     59     if (this != &rhs) {
     60       // Delete the currently owned UTF chars.
     61       this->~ScopedUtfChars();
     62 
     63       // Move the rhs ScopedUtfChars and zero it out.
     64       env_ = rhs.env_;
     65       string_ = rhs.string_;
     66       utf_chars_ = rhs.utf_chars_;
     67       rhs.env_ = nullptr;
     68       rhs.string_ = nullptr;
     69       rhs.utf_chars_ = nullptr;
     70     }
     71     return *this;
     72   }
     73 
     74   const char* c_str() const {
     75     return utf_chars_;
     76   }
     77 
     78   size_t size() const {
     79     return strlen(utf_chars_);
     80   }
     81 
     82   const char& operator[](size_t n) const {
     83     return utf_chars_[n];
     84   }
     85 
     86  private:
     87   JNIEnv* env_;
     88   jstring string_;
     89   const char* utf_chars_;
     90 
     91   DISALLOW_COPY_AND_ASSIGN(ScopedUtfChars);
     92 };
     93 
     94 #endif  // SCOPED_UTF_CHARS_H_
     95