istreamwrapper.h

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// Tencent is pleased to support the open source community by making RapidJSON available.
// 
// Copyright (C) 2015 THL A29 Limited, a Tencent company, and Milo Yip. All rights reserved.
//
// Licensed under the MIT License (the "License"); you may not use this file except
// in compliance with the License. You may obtain a copy of the License at
//
// http://opensource.org/licenses/MIT
//
// Unless required by applicable law or agreed to in writing, software distributed 
// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR 
// CONDITIONS OF ANY KIND, either express or implied. See the License for the 
// specific language governing permissions and limitations under the License.

#ifndef RAPIDJSON_ISTREAMWRAPPER_H_
#define RAPIDJSON_ISTREAMWRAPPER_H_

#include "stream.h"
#include <iosfwd>

#ifdef __clang__
RAPIDJSON_DIAG_PUSH
RAPIDJSON_DIAG_OFF(padded)
#elif defined(_MSC_VER)
RAPIDJSON_DIAG_PUSH
RAPIDJSON_DIAG_OFF(4351) // new behavior: elements of array 'array' will be default initialized
#endif

RAPIDJSON_NAMESPACE_BEGIN

//! Wrapper of \c std::basic_istream into RapidJSON's Stream concept.
/*!
    The classes can be wrapped including but not limited to:

    - \c std::istringstream
    - \c std::stringstream
    - \c std::wistringstream
    - \c std::wstringstream
    - \c std::ifstream
    - \c std::fstream
    - \c std::wifstream
    - \c std::wfstream

    \tparam StreamType Class derived from \c std::basic_istream.
*/
   
template <typename StreamType>
class BasicIStreamWrapper {
public:
    typedef typename StreamType::char_type Ch;
    BasicIStreamWrapper(StreamType& stream) : stream_(stream), count_(), peekBuffer_() {}

    Ch Peek() const { 
        typename StreamType::int_type c = stream_.peek();
        return RAPIDJSON_LIKELY(c != StreamType::traits_type::eof()) ? static_cast<Ch>(c) : static_cast<Ch>('\0');
    }

    Ch Take() { 
        typename StreamType::int_type c = stream_.get();
        if (RAPIDJSON_LIKELY(c != StreamType::traits_type::eof())) {
            count_++;
            return static_cast<Ch>(c);
        }
        else
            return '\0';
    }

    // tellg() may return -1 when failed. So we count by ourself.
    size_t Tell() const { return count_; }

    Ch* PutBegin() { RAPIDJSON_ASSERT(false); return 0; }
    void Put(Ch) { RAPIDJSON_ASSERT(false); }
    void Flush() { RAPIDJSON_ASSERT(false); }
    size_t PutEnd(Ch*) { RAPIDJSON_ASSERT(false); return 0; }

    // For encoding detection only.
    const Ch* Peek4() const {
        RAPIDJSON_ASSERT(sizeof(Ch) == 1); // Only usable for byte stream.
        int i;
        bool hasError = false;
        for (i = 0; i < 4; ++i) {
            typename StreamType::int_type c = stream_.get();
            if (c == StreamType::traits_type::eof()) {
                hasError = true;
                stream_.clear();
                break;
            }
            peekBuffer_[i] = static_cast<Ch>(c);
        }
        for (--i; i >= 0; --i)
            stream_.putback(peekBuffer_[i]);
        return !hasError ? peekBuffer_ : 0;
    }

private:
    BasicIStreamWrapper(const BasicIStreamWrapper&);
    BasicIStreamWrapper& operator=(const BasicIStreamWrapper&);

    StreamType& stream_;
    size_t count_;  //!< Number of characters read. Note:
    mutable Ch peekBuffer_[4];
};

typedef BasicIStreamWrapper<std::istream> IStreamWrapper;
typedef BasicIStreamWrapper<std::wistream> WIStreamWrapper;

#if defined(__clang__) || defined(_MSC_VER)
RAPIDJSON_DIAG_POP
#endif

RAPIDJSON_NAMESPACE_END

#endif // RAPIDJSON_ISTREAMWRAPPER_H_