为什么字符<<和字符>>中间结果 int

Why are char << and char >> intermediate results int

本文关键字：gt lt 字符 int 结果 为什么 中间      更新时间：2023-10-16

>cygwin gcc 4.5.3

我正在尝试确定C++中各种计算中使用的中间结果。对于"char"，我得到以下结果（x 是一个字符）：

x op y is of type char if y is a char/unsigned char
x op y is of type y otherwise except if op is left/right shift

对于左/右移位，中间结果的类型为"int"，这与所有其他计算相反。这是标准实现吗？

以下是使用的代码（不要对此太兴奋）：

# include <iostream>
# include <iomanip>
# include <typeinfo>
# include "cstdio"
# include <cstdlib>
using namespace std;
typedef unsigned char  UCHAR;
typedef unsigned short USHORT;
typedef unsigned int   INT;
typedef unsigned long  ULONG;
string find(type_info* info) {
   struct type {
      type_info* typeInfo;
      string     name;
   };
   int i;
   static type types[] = { {const_cast<type_info*>(&typeid(bool)),   " BOOL"  }
                         , {const_cast<type_info*>(&typeid(char)),   " CHAR"  }
                         , {const_cast<type_info*>(&typeid(UCHAR)),  " UCHAR" }
                         , {const_cast<type_info*>(&typeid(short)),  " SHORT" }
                         , {const_cast<type_info*>(&typeid(USHORT)), " USHORT"}
                         , {const_cast<type_info*>(&typeid(int)),    " INT"   }
                         , {const_cast<type_info*>(&typeid(uint)),   " UINT"  }
                         , {const_cast<type_info*>(&typeid(long)),   " LONG"  }
                         , {const_cast<type_info*>(&typeid(ULONG)),  " ULONG" }
                         };
   for(i = 0; i < sizeof(types)/sizeof(types[0]); i++ )
      if (types[i].typeInfo == info) break;
   if (i >= sizeof(types)/sizeof(types[0])) return " NOT FOUND";
   return types[i].name;
}
void func0(char x) {
   ios_base::fmtflags ioFlags = cout.flags();
   string info = find(const_cast<type_info*>(&typeid(x)));
   char save = x;
   cout << "func0(char " << (long)x << ')' << endl;
   cout << "!x  " << setw(12) << (!x)    << " 0x" << setw(8) << setfill('0') << hex << (!x) <<  find(const_cast<type_info*>(&typeid(!x))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "~x  " << setw(12) << (~x)    << " 0x" << setw(8) << setfill('0') << hex << (~x) <<  find(const_cast<type_info*>(&typeid(~x))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "+x  " << setw(12) << (+x)    << " 0x" << setw(8) << setfill('0') << hex << (+x) <<  find(const_cast<type_info*>(&typeid(+x))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "-x  " << setw(12) << (-x)    << " 0x" << setw(8) << setfill('0') << hex << (-x) <<  find(const_cast<type_info*>(&typeid(-x))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "++x " << setw(12) << (long)(++x)    << " 0x" << setw(8) << setfill('0') << hex << (++x) <<  find(const_cast<type_info*>(&typeid(++x))) << endl;
   cout.flags(ioFlags); cout << setfill(' '); x = save;
   cout << "--x " << setw(12) << (long)(--x)    << " 0x" << setw(8) << setfill('0') << hex << (--x) <<  find(const_cast<type_info*>(&typeid(--x))) << endl;
   cout.flags(ioFlags); cout << setfill(' '); x = save;
   cout << "x++ " << setw(12) << (long)(x++)    << " 0x" << setw(8) << setfill('0') << hex << (x++) <<  find(const_cast<type_info*>(&typeid(x++))) << endl;
   cout.flags(ioFlags); cout << setfill(' '); x = save;
   cout << "x-- " << setw(12) << (long)(x--)    << " 0x" << setw(8) << setfill('0') << hex << (x--) <<  find(const_cast<type_info*>(&typeid(x--))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << endl;
}
void func1(char x, char y) {
   ios_base::fmtflags ioFlags = cout.flags();
   cout << "func1(char " << (signed long)x << ", char " << (unsigned long)y << ')' << endl;
   cout << "x  + y " << setw(12) << (x  + y) << " 0x" << setw(8) << setfill('0') << hex << (x  + y) <<  find(const_cast<type_info*>(&typeid(x + y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  - y " << setw(12) << (x  - y) << " 0x" << setw(8) << setfill('0') << hex << (x  - y) <<  find(const_cast<type_info*>(&typeid(x - y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  * y " << setw(12) << (x  * y) << " 0x" << setw(8) << setfill('0') << hex << (x  * y) <<  find(const_cast<type_info*>(&typeid(x * y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   if (y == 0) {
        cout << "x  / y " << x << " / 0" <<  endl;
   } else {
        cout << "x  / y " << setw(12) << (x  / y) << " 0x" << setw(8) << setfill('0') << hex << (x / y) <<  find(const_cast<type_info*>(&typeid(x / y))) << endl;
   }
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x %  y " << setw(12) << (x  & y) << " 0x" << setw(8) << setfill('0') << hex << (x  & y) <<  find(const_cast<type_info*>(&typeid(x  & y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x << y " << setw(12) << (x << y) << " 0x" << setw(8) << setfill('0') << hex << (x << y) <<  find(const_cast<type_info*>(&typeid(x << y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x >> y " << setw(12) << (x >> y) << " 0x" << setw(8) << setfill('0') << hex << (x >> y) <<  find(const_cast<type_info*>(&typeid(x >> y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  & y " << setw(12) << (x  & y) << " 0x" << setw(8) << setfill('0') << hex << (x  & y) <<  find(const_cast<type_info*>(&typeid(x  & y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  | y " << setw(12) << (x  | y) << " 0x" << setw(8) << setfill('0') << hex << (x  | y) <<  find(const_cast<type_info*>(&typeid(x  | y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  ^ x " << setw(12) << (x  ^ y) << " 0x" << setw(8) << setfill('0') << hex << (x  ^ y) <<  find(const_cast<type_info*>(&typeid(x  ^ y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << endl;
}
void func1(char x, unsigned char y) {
   ios_base::fmtflags ioFlags = cout.flags();
   cout << "func1(char " << (signed long)x << ", uchar " << (unsigned long)y << ')' << endl;
   cout << "x  + y " << setw(12) << (x  + y) << " 0x" << setw(8) << setfill('0') << hex << (x  + y) <<  find(const_cast<type_info*>(&typeid(x + y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  - y " << setw(12) << (x  - y) << " 0x" << setw(8) << setfill('0') << hex << (x  - y) <<  find(const_cast<type_info*>(&typeid(x - y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  * y " << setw(12) << (x  * y) << " 0x" << setw(8) << setfill('0') << hex << (x  * y) <<  find(const_cast<type_info*>(&typeid(x * y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   if (y == 0) {
        cout << "x  / y " << x << " / 0" <<  endl;
   } else {
        cout << "x  / y " << setw(12) << (x  / y) << " 0x" << setw(8) << setfill('0') << hex << (x / y) <<  find(const_cast<type_info*>(&typeid(x / y))) << endl;
   }
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x %  y " << setw(12) << (x  & y) << " 0x" << setw(8) << setfill('0') << hex << (x  & y) <<  find(const_cast<type_info*>(&typeid(x  & y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x << y " << setw(12) << (x << y) << " 0x" << setw(8) << setfill('0') << hex << (x << y) <<  find(const_cast<type_info*>(&typeid(x << y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x >> y " << setw(12) << (x >> y) << " 0x" << setw(8) << setfill('0') << hex << (x >> y) <<  find(const_cast<type_info*>(&typeid(x >> y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  & y " << setw(12) << (x  & y) << " 0x" << setw(8) << setfill('0') << hex << (x  & y) <<  find(const_cast<type_info*>(&typeid(x  & y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  | y " << setw(12) << (x  | y) << " 0x" << setw(8) << setfill('0') << hex << (x  | y) <<  find(const_cast<type_info*>(&typeid(x  | y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  ^ x " << setw(12) << (x  ^ y) << " 0x" << setw(8) << setfill('0') << hex << (x  ^ y) <<  find(const_cast<type_info*>(&typeid(x  ^ y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << endl;
}
void func1(char x, unsigned long y) {
   ios_base::fmtflags ioFlags = cout.flags();
   cout << "func1(char " << (signed long)x << ", ulong " << y << ')' << endl;
   cout << "x  + y " << setw(12) << (x  + y) << " 0x" << setw(8) << setfill('0') << hex << (x  + y) <<  find(const_cast<type_info*>(&typeid(x + y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  - y " << setw(12) << (x  - y) << " 0x" << setw(8) << setfill('0') << hex << (x  - y) <<  find(const_cast<type_info*>(&typeid(x - y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  * y " << setw(12) << (x  * y) << " 0x" << setw(8) << setfill('0') << hex << (x  * y) <<  find(const_cast<type_info*>(&typeid(x * y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   if (y == 0) {
        cout << "x  / y " << x << " / 0" <<  endl;
   } else {
        cout << "x  / y " << setw(12) << (x  / y) << " 0x" << setw(8) << setfill('0') << hex << (x / y) <<  find(const_cast<type_info*>(&typeid(x / y))) << endl;
   }
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x %  y " << setw(12) << (x  & y) << " 0x" << setw(8) << setfill('0') << hex << (x  & y) <<  find(const_cast<type_info*>(&typeid(x  & y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x << y " << setw(12) << (x << y) << " 0x" << setw(8) << setfill('0') << hex << (x << y) <<  find(const_cast<type_info*>(&typeid(x << y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x >> y " << setw(12) << (x >> y) << " 0x" << setw(8) << setfill('0') << hex << (x >> y) <<  find(const_cast<type_info*>(&typeid(x >> y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  & y " << setw(12) << (x  & y) << " 0x" << setw(8) << setfill('0') << hex << (x  & y) <<  find(const_cast<type_info*>(&typeid(x  & y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  | y " << setw(12) << (x  | y) << " 0x" << setw(8) << setfill('0') << hex << (x  | y) <<  find(const_cast<type_info*>(&typeid(x  | y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  ^ x " << setw(12) << (x  ^ y) << " 0x" << setw(8) << setfill('0') << hex << (x  ^ y) <<  find(const_cast<type_info*>(&typeid(x  ^ y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << endl;
}
void func1(char x, long y) {
   ios_base::fmtflags ioFlags = cout.flags();
   cout << "func1(char " << (signed long)x << ", long " << y << ')' << endl;
   cout << "x  + y " << setw(12) << (x  + y) << " 0x" << setw(8) << setfill('0') << hex << (x  + y) <<  find(const_cast<type_info*>(&typeid(x + y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  - y " << setw(12) << (x  - y) << " 0x" << setw(8) << setfill('0') << hex << (x  - y) <<  find(const_cast<type_info*>(&typeid(x - y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  * y " << setw(12) << (x  * y) << " 0x" << setw(8) << setfill('0') << hex << (x  * y) <<  find(const_cast<type_info*>(&typeid(x * y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   if (y == 0) {
        cout << "x  / y " << x << " / 0" <<  endl;
   } else {
        cout << "x  / y " << setw(12) << (x  / y) << " 0x" << setw(8) << setfill('0') << hex << (x / y) <<  find(const_cast<type_info*>(&typeid(x / y))) << endl;
   }
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x %  y " << setw(12) << (x  & y) << " 0x" << setw(8) << setfill('0') << hex << (x  & y) <<  find(const_cast<type_info*>(&typeid(x  & y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x << y " << setw(12) << (x << y) << " 0x" << setw(8) << setfill('0') << hex << (x << y) <<  find(const_cast<type_info*>(&typeid(x << y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x >> y " << setw(12) << (x >> y) << " 0x" << setw(8) << setfill('0') << hex << (x >> y) <<  find(const_cast<type_info*>(&typeid(x >> y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  & y " << setw(12) << (x  & y) << " 0x" << setw(8) << setfill('0') << hex << (x  & y) <<  find(const_cast<type_info*>(&typeid(x  & y))) << endl;
cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  | y " << setw(12) << (x  | y) << " 0x" << setw(8) << setfill('0') << hex << (x  | y) <<  find(const_cast<type_info*>(&typeid(x  | y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << "x  ^ x " << setw(12) << (x  ^ y) << " 0x" << setw(8) << setfill('0') << hex << (x  ^ y) <<  find(const_cast<type_info*>(&typeid(x  ^ y))) << endl;
   cout.flags(ioFlags); cout << setfill(' ');
   cout << endl;
}
int main(int argc, char** argv) {
   char x = -1;
   func0((char) 1);
   func1(x, (char) 1);
   func1(x, (unsigned char) 1);
   func1(x, (long) 1);
   func1(x, (unsigned long) 1);
   sleep(1);
   return 0;
}

你最初的结论是不正确的。C/C++中的所有算术运算至少在大小int（或者，也许是unsigned int）的域内执行计算。所有较小的操作数类型（char、short等）在任何实际计算开始之前都会提升为 int，并且结果的类型为 int 。只有++和--的前缀和后缀版本等操作才会保留其操作数的类型。

这适用于二进制+、*、-等操作。这也适用于<<和>>。因此，<<和>>与其他算术运算符没有任何不同。

你是如何得出结论，"x op y is of type char if y is a char/unsigned char"我不是很清楚的。我刚刚运行了您的代码，它确认了预期的行为：只有像 ++ 和 -- 这样的操作计算为char类型，而char参数的所有其他操作的计算结果为int值。

通过在顶部添加以下内容来编译代码后，

typedef unsigned uint; //!
void sleep( int ) {} //!
#include <string> //!

仍然有一些正式的UB，但应该无关紧要。

然而，结果并未表明

"x op y 是字符类型，如果 y 是字符/无符号字符
x op y 是 y 型，否则除非 op 是左/右移位"

您使用什么编译器？

你问，

"这是标准实现吗？"

嗯，不，没有标准的实现。只有一个ISO标准。

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