期待eof，但相當任意的數據附近eof

Question

我試圖找出不需要的尾端數據在一個文件中的原因我正在寫入特定的數據，並不相信我寫入文件時發生錯誤。

輸出看起來像：

building  room_numbr capacity 

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

的Attempt to seek file pointer error是正常的，因爲它代表試圖移動文件指針上的無效流時拋出異常。但是，ÿÿÿÿÿÿÿÿÿÿ不是正常的，也不是以固定大小的文件格式使用10或20字節來寫入數據。

創建文件的位置：

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; 
    } 

} 

將數據寫入到文件

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; 
} 
} 

讀取數據文件的位置：讀取該文件，並將結果打印到屏幕

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; 
} 

} 

代碼：

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"; 

    } 

} 

Answer 1

std::ifstream::get返回std::char_traits<char>::eof失敗，通常具有int值-1。如果你把它理解爲一個有效的字符並且轉換爲char，那麼你會得到'\xff'，這在ISO-8859-15中是ÿ。

當您從文件中讀取字符時，尤其是在查找後，您應該檢查eof和/或eofbit。