std :: basic_ifstream throws std :: bad_cast [英] std::basic_ifstream throws std::bad_cast

问题描述

我想使用下面的代码从文件中读取数据。 （注意，您需要在GCC上启用C ++ 11功能来进行此编译。）

  #include< fstream& 
 
 typedef unsigned char byte; 
 
 int main（）
 {
 std :: string filename =test.cpp; 
 std :: basic_ifstream< byte> in（filename，std :: basic_ifstream< byte> :: in | std :: basic_ifstream< byte> :: binary）; 
 in.exceptions（std :: ios :: failbit | std :: ios :: badbit）; 
 byte buf [5]; 
 in.read（buf，5）; 
 return 0;但是，当读取数据时，我得到一个例外：
在抛出'std :: bad_cast'实例后调用
 what（）：std :: bad_cast 
当调用 in.read（buf，5）命令时，会发生这种情况。
 
 
 
知道我可以通过不设置异常掩码我设置，但这不能解决这个问题，它只能掩盖这个异常。没有异常掩码，代码保持工作，但是0个字符被读取。
 
 
 
有人知道为什么抛出这个异常吗？ 
解决方案
 c ++ STL仅包含char_traits的两个特殊化：
  struct char_traits< char> ;; 
 struct char_traits< wchar_t> ;; 
 
对于发布的代码， char_traits< byte& code>是必需的。
 
 
 
有关此SO问题 
 
I am trying to read data from a file using below code. (Note that you need to enable C++11 features on GCC to make this compile.)
#include <fstream>

typedef unsigned char byte;

int main()
{
    std::string filename = "test.cpp";
    std::basic_ifstream<byte> in(filename, std::basic_ifstream<byte>::in | std::basic_ifstream<byte>::binary);
    in.exceptions(std::ios::failbit | std::ios::badbit);
    byte buf[5];
    in.read(buf, 5);
    return 0;
}
However, when reading data I get an exception:
terminate called after throwing an instance of 'std::bad_cast'
  what():  std::bad_cast
This happens when the in.read(buf, 5) command is invoked.

I know that I can suppress this exception by not setting the exception mask I set but this does not fix the problem, it only masks it. Without an exception mask, the code keeps working but 0 characters are read.

Does anyone know why this exception is thrown? And how do I make it go away?
解决方案
c++ STL only contains two specializations of char_traits:
   struct char_traits < char >;
   struct char_traits <wchar_t >;
For the code posted to work a definition of char_traits<byte> is required.

More details in this SO question

                        
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