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我试图找出我正在写入特定数据的文件中不需要的尾随数据的原因,并且不相信我在写入文件时犯了错误。

输出如下所示:

building     room_numbr   capacity

packard    | 101        | 500        |
painter    | 514        | 10         |
ÿÿÿÿÿÿÿÿÿÿ | Attempt to seek file pointer error

Attempt to seek file pointer error是正常的,因为它表示尝试在无效流上移动文件指针时引发的异常。但是,ÿÿÿÿÿÿÿÿÿÿ使用 10 或 20 字节写入数据的固定大小文件格式既不正常也不预期。

在此处创建文件:

BinarySearchFile::BinarySearchFile(std::string file_name){

    // concatenate extension to fileName
    file_name += ".dat";

    // form complete table data filename
    data_file_name = file_name;

    // create or reopen table data file for reading and writing
    binary_search_file.open(data_file_name,  std::ios::out | std::ios::in | std::ios::app); 

    if(!binary_search_file.is_open()){

        binary_search_file.clear();
        binary_search_file.open(data_file_name, std::ios::out);
        binary_search_file.close();
        binary_search_file.open(data_file_name, std::ios::out | std::ios::in | std::ios::app);
    }

    try{
        if(binary_search_file.fail()){
            throw CustomException("Unspecified table data file error");
        }
    }
    catch (CustomException &custom_exception){  // Using custom exception class
        std::cout << custom_exception.what() << std::endl;
        return;
    }   

}

将数据写入文件

void BinarySearchFile::writeT(std::string attribute){
try{
    if(binary_search_file){
        for(auto start = attribute.begin(); start != attribute.end();  ++start){
            binary_search_file.put(' ');
            binary_search_file.put(*start);
        }
        binary_search_file.flush();
        /*
        attribute.resize(attribute.length() * 2);
        const char *write_this = attribute.data();
        binary_search_file.write(write_this, attribute.length());
        */
    }else if(binary_search_file.fail()){
        throw CustomException("Attempt to write attribute error");
    }

}
catch(CustomException &custom_exception){  // Using custom exception class
    std::cout << custom_exception.what() << std::endl;
    return;
}
}

在此处读取数据文件:

   std::string BinarySearchFile::readT(long file_pointer_location, long size_of_data) 
{
try{
    if(binary_search_file){

        std::string data = "";
        binary_search_file.seekp(file_pointer_location);
        binary_search_file.seekg(file_pointer_location);
        while (size_of_data > 0 ){
            binary_search_file.get();
            data += binary_search_file.get();
            size_of_data -= 2;
        }

        /*
        char data[20];
        binary_search_file.seekp(filePointerLocation);
        binary_search_file.seekg(filePointerLocation);
        binary_search_file.read(data, sizeOfData);
        */
        return data;
    }else if(binary_search_file.fail()){
        throw CustomException("Attempt to read attribute error");
    }

}
catch(CustomException &custom_exception){  // Using custom exception class
    std::cout << custom_exception.what() << std::endl;
}

}

读取文件并将结果打印到屏幕的代码:

while(true){

    //reinitialize the catalog pointer to the beginning 
    catalog->setPointerBegin();

    //display data
    do{
        if (boost::iequals((domain = catalog->getAttributeDomain()), "string")){
            if(dataFile->binary_search_file_status()){
                std::cout << dataFile->read_data(filePointer, 20) << " | ";
                if (!writer_.fail())
                    writer_ << dataFile->read_data(filePointer, 20) << " | ";
            }
            else{
                std::cout << "\n";
                if (!writer_.fail())
                    writer_ << "\n";

                        return true;
                }
                // update the file pointer
                filePointer += 20;
                dataFile->set_file_pointer(filePointer);
            }
            else{
                if(dataFile->binary_search_file_status()){
                    std::cout << dataFile->read_data(filePointer, 10);
                    if (!writer_.fail())
                        writer_ << dataFile->read_data(filePointer, 10);
                    for(int i = 0; i < 5; i++){
                            std::cout << " ";
                            if (!writer_.fail())
                                writer_ << " ";
                        }
                        std::cout << " | ";
                        if (!writer_.fail()){
                            writer_ << " | ";
                    }
                }
                else{
                    std::cout << "\n";
                    if (!writer_.fail()){
                        writer_ << "\n";
                    }
                    return true;
                }
                // update the file pointer
                filePointer += 10;

                }       


            } while(catalog->traverseForward() != nullptr);

            std::cout << "\n";
            if (!writer_.fail())
                writer_ << "\n";

    }

}   
4

1 回答 1

3

std::ifstream::get失败时返回std::char_traits<char>::eof,通常int-1. 如果您盲目地将其解释为有效字符并转换为char,您将得到'\xff',在 ISO-8859-15 中是ÿ.

您应该检查eof和/或eofbit何时从文件中读取字符,尤其是在查找之后。

于 2013-05-03T21:00:47.083 回答