爲什麼unsigned char *與ifstream :: read一起工作？

Question

我是一名C++初學者。我有一個新的項目，我必須學習它，所以我嘗試了一些東西來測試我的理解。對於這個問題，我試圖讀取一個文件，然後在屏幕上打印出來。超級簡單，只是爲了善於理解並理解我正在使用的功能。我將MS Word文檔中的一些文本複製到記事本（* .txt）文件中，並試圖讀取此* .txt文件。 word文檔中的所有文本都以粗體顯示，但除此之外沒有「不尋常」字符。除了加粗的「 - 」符號外，所有內容都會顯示在屏幕上。該字符被打印爲帶有帽子字符的「u」（「所謂的擴展ASCII」代碼150）。我嘗試打印出我的數組中的這個字符的整數值（應該是150），但是我得到了-106。我意識到這個有符號整數與無符號整數150的位數相同。我的問題是如何讓輸出結果爲150？這裏是我的代碼：

 #include <iostream> 
     #include <fstream> 
     using namespace std; 

     int main() { 
     unsigned char* input1; 
     int input1size = 57; 
     ifstream file("hello_world2.txt",ios::binary | ios::ate); 
     if (file.is_open()){ 
      int size; 
      size = (int) file.tellg(); 
      cout <<"This file is " << size << " bytes." << endl; 
      file.seekg(0,ios::beg); 
      input1 = new unsigned char[input1size]; 
      file.read(input1, input1size); 
      cout << "The first " << input1size <<" characters of this file are:" << endl<<endl; 
      for (int i=0; i<input1size; i++) { 
      cout << input1[i]; 
     } 
     cout<<endl; 
     } 
     else { 
     cout <<"Unable to open file" << endl; 
     int paus; 
     cin>>paus; 
     return 0; 
     } 
     file.close(); 
     int charcheck = 25; 
     int a=0; 
     int a1=0; 
     int a2=0; 
     unsigned int a3=0; 
     unsigned short int a4=0; 
     short int a5=0; 
     a = input1[charcheck]; 
     a1 = input1[charcheck-1]; 
     a2 = input1[charcheck+1]; 
     a3 = input1[charcheck]; 
     a4 = input1[charcheck]; 
     a5 = input1[charcheck]; 
     cout <<endl<<"ASCII code for char in input1[" << charcheck-1 <<"] is: " << a1 << endl; 
     cout <<endl<<"ASCII code for char in input1[" << charcheck <<"] is: " << a << endl; 
     cout <<endl<<"ASCII code for char in input1[" << charcheck+1 <<"] is: " << a2 << endl; 
     cout <<endl<<"ASCII code for char in input1[" << charcheck <<"] as unsigned int: " << a3 << endl; 
     cout <<endl<<"ASCII code for char in input1[" << charcheck <<"] as unsigned short int: " << a4 << endl; 
     cout <<endl<<"ASCII code for char in input1[" << charcheck <<"] as short int: " << a5 << endl; 
     int paus; 
     cin>>paus; 
     return 0; 
     } 

輸出這一切看起來像：

This file is 80 bytes. 
    The first 57 characters of this file are: 

    STATUS REPORT 
    PERIOD 01 u 31 JUL 09 

    TASK 310: APPLIC 

    ASCII code for char in input1[24] is: 32 
    ASCII code for char in input1[25] is: -106 
    ASCII code for char in input1[26] is: 32 
    ASCII code for char in input1[25] as unsigned int: 4294967190 
    ASCII code for char in input1[25] as unsigned short int: 65430 
    ASCII code for char in input1[25] as short int: -106 

所以纔出現「詮釋了」總是讀爲簽署。當我嘗試使「a」無符號時，它將字符的八位左邊的所有位都變爲1。爲什麼是這樣？對不起，問題的長度，只是試圖詳細。謝謝！

Answer 1

你正在處理的是當你將字符賦值給你的一個字符時將字符提升爲int的符號擴展？變量。

所有的高位必須設置爲1，以保持它與char的較小存儲區中的負值相同。