从'(signed) -1'到'unsigned long'的转换是否标准化？
Is the conversion from '(signed) -1' to 'unsigned long' standardized?
在, you can find 中：
Strictly speaking the bit representations of the two numbers before conversion being the same doesn't matter. Even with 1's complement or signed magnitude representations, the conversion of (signed) -1 to unsigned long will always result in ULONG_MAX. (The bit pattern will be the same after conversion of course).
我知道你可以用其他方式来代表 -1 除了 Two's Compliment，这是一个有效的补充，应该在我的回答中。但是，在这样的实现中，依赖到 ULONG_MAX 的转换是否安全？
评论者正确；从任何其他整数类型到无符号整数类型的转换始终是明确定义的。如果无符号整数类型的范围是 0 到 2^N - 1，那么转换的结果将是原始值减模 2^N。即使（如在具有一个补码或符号幅度表示的系统中）所说的约简模 2^N 需要额外的指令，情况也是如此。
是的，无论实际表示如何，都可以保证：
[conv.integral]（强调我的）
A prvalue of an integer type can be converted to a prvalue of another
integer type. A prvalue of an unscoped enumeration type can be
converted to a prvalue of an integer type.
If the destination type is unsigned, the resulting value is the least unsigned integer congruent to the source integer (modulo 2n
where n is the number of bits used to represent the unsigned type).
[ Note: In a two's complement representation, this conversion is
conceptual and there is no change in the bit pattern (if there is no
truncation). — end note ]
在
Strictly speaking the bit representations of the two numbers before conversion being the same doesn't matter. Even with 1's complement or signed magnitude representations, the conversion of (signed) -1 to unsigned long will always result in
ULONG_MAX. (The bit pattern will be the same after conversion of course).
我知道你可以用其他方式来代表 -1 除了 Two's Compliment，这是一个有效的补充，应该在我的回答中。但是，在这样的实现中，依赖到 ULONG_MAX 的转换是否安全？
评论者正确；从任何其他整数类型到无符号整数类型的转换始终是明确定义的。如果无符号整数类型的范围是 0 到 2^N - 1，那么转换的结果将是原始值减模 2^N。即使（如在具有一个补码或符号幅度表示的系统中）所说的约简模 2^N 需要额外的指令，情况也是如此。
是的，无论实际表示如何，都可以保证：
[conv.integral]（强调我的）
A prvalue of an integer type can be converted to a prvalue of another integer type. A prvalue of an unscoped enumeration type can be converted to a prvalue of an integer type.
If the destination type is unsigned, the resulting value is the least unsigned integer congruent to the source integer (modulo 2n where
nis the number of bits used to represent the unsigned type). [ Note: In a two's complement representation, this conversion is conceptual and there is no change in the bit pattern (if there is no truncation). — end note ]