Home | History | Annotate | Download | only in nativehelper 
      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_included
     18 #define SCOPED_UTF_CHARS_H_included
     19 
     20 #include "JNIHelp.h"
     21 #include <string.h>
     22 
     23 // A smart pointer that provides read-only access to a Java string's UTF chars.
     24 // Unlike GetStringUTFChars, we throw NullPointerException rather than abort if
     25 // passed a null jstring, and c_str will return nullptr.
     26 // This makes the correct idiom very simple:
     27 //
     28 //   ScopedUtfChars name(env, java_name);
     29 //   if (name.c_str() == nullptr) {
     30 //     return nullptr;
     31 //   }
     32 class ScopedUtfChars {
     33  public:
     34   ScopedUtfChars(JNIEnv* env, jstring s) : env_(env), string_(s) {
     35     if (s == nullptr) {
     36       utf_chars_ = nullptr;
     37       jniThrowNullPointerException(env, nullptr);
     38     } else {
     39       utf_chars_ = env->GetStringUTFChars(s, nullptr);
     40     }
     41   }
     42 
     43   ScopedUtfChars(ScopedUtfChars&& rhs) :
     44       env_(rhs.env_), string_(rhs.string_), utf_chars_(rhs.utf_chars_) {
     45     rhs.env_ = nullptr;
     46     rhs.string_ = nullptr;
     47     rhs.utf_chars_ = nullptr;
     48   }
     49 
     50   ~ScopedUtfChars() {
     51     if (utf_chars_) {
     52       env_->ReleaseStringUTFChars(string_, utf_chars_);
     53     }
     54   }
     55 
     56   ScopedUtfChars& operator=(ScopedUtfChars&& rhs) {
     57     if (this != &rhs) {
     58       // Delete the currently owned UTF chars.
     59       this->~ScopedUtfChars();
     60 
     61       // Move the rhs ScopedUtfChars and zero it out.
     62       env_ = rhs.env_;
     63       string_ = rhs.string_;
     64       utf_chars_ = rhs.utf_chars_;
     65       rhs.env_ = nullptr;
     66       rhs.string_ = nullptr;
     67       rhs.utf_chars_ = nullptr;
     68     }
     69     return *this;
     70   }
     71 
     72   const char* c_str() const {
     73     return utf_chars_;
     74   }
     75 
     76   size_t size() const {
     77     return strlen(utf_chars_);
     78   }
     79 
     80   const char& operator[](size_t n) const {
     81     return utf_chars_[n];
     82   }
     83 
     84  private:
     85   JNIEnv* env_;
     86   jstring string_;
     87   const char* utf_chars_;
     88 
     89   DISALLOW_COPY_AND_ASSIGN(ScopedUtfChars);
     90 };
     91 
     92 #endif  // SCOPED_UTF_CHARS_H_included
     93