1 /*
2  * Copyright (C) 2009 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 LOCAL_ARRAY_H_included
18 #define LOCAL_ARRAY_H_included
19 
20 #include <cstddef>
21 #include <new>
22 
23 /**
24  * A fixed-size array with a size hint. That number of bytes will be allocated
25  * on the stack, and used if possible, but if more bytes are requested at
26  * construction time, a buffer will be allocated on the heap (and deallocated
27  * by the destructor).
28  *
29  * The API is intended to be a compatible subset of C++0x's std::array.
30  */
31 template <size_t STACK_BYTE_COUNT>
32 class LocalArray {
33 public:
34     /**
35      * Allocates a new fixed-size array of the given size. If this size is
36      * less than or equal to the template parameter STACK_BYTE_COUNT, an
37      * internal on-stack buffer will be used. Otherwise a heap buffer will
38      * be allocated.
39      */
LocalArray(size_t desiredByteCount)40     LocalArray(size_t desiredByteCount) : mSize(desiredByteCount) {
41         if (desiredByteCount > STACK_BYTE_COUNT) {
42             mPtr = new char[mSize];
43         } else {
44             mPtr = &mOnStackBuffer[0];
45         }
46     }
47 
48     /**
49      * Frees the heap-allocated buffer, if there was one.
50      */
~LocalArray()51     ~LocalArray() {
52         if (mPtr != &mOnStackBuffer[0]) {
53             delete[] mPtr;
54         }
55     }
56 
57     // Capacity.
size()58     size_t size() { return mSize; }
empty()59     bool empty() { return mSize == 0; }
60 
61     // Element access.
62     char& operator[](size_t n) { return mPtr[n]; }
63     const char& operator[](size_t n) const { return mPtr[n]; }
64 
65 private:
66     char mOnStackBuffer[STACK_BYTE_COUNT];
67     char* mPtr;
68     size_t mSize;
69 
70     // Disallow copy and assignment.
71     LocalArray(const LocalArray&);
72     void operator=(const LocalArray&);
73 };
74 
75 #endif // LOCAL_ARRAY_H_included
76