隐式数字类型转换的规则

Question

我有几个关于带有符号和无符号变量的类型转换的问题。 在这种情况下将选择哪种类型 signed int + unsigned int = ??? 那么当代替变量我有常量时的情况呢

x1(unsigned int) = x1(unsigned int) - 0xFFFFFFFA

我读过类似常量的内容unsigned ints，除非明确写成0xFFFFFFFA(UL)。然后

1) unsigned int - unsigned int = unsigned int
2) unsigned int = unsigned int

如果浮点数为

，该怎么办？

 x1(unsigned int) = x2(signed short int) + x3(unsigned int) + x4(unsigned short int) 
 * 0.1(float);  
 1)float * unsigned short int = float
 2)float + unsigned int = float 
 3)float + signed short int = float
 4)unsigned int = (unsigned int)float

我想这是＆＃39; a＆＃39;将是char

signed int = 'a' + signed short int - signed int 
1) 'a' + signed short int = int ???
2) int - signed int = int ???
3) signed int = (signed int) int ???

还有一个

long double = signed int + wchar_t - unsigned int * 10 
1)unsigned int * 10(int) = int
2)wchar_t - int = int
3)signed int + int = int 
4)long double = (long double) int

Answer 1

你可以随时使用我评论过的技巧：

struct {} _ = some_expression;

编译器错误会告诉您表达式的确切类型。

对于背景资料，请参阅http://cppreference.com，特别是Implicit Conversion

• Numeric Promotions

• Numeric Conversions

您还应该阅读标准中的conv.prom和conv.double。