将 unsigned int 的最大值转换为 int 并期望结果为 -1 是否可移植？
Is it portable to cast the max value of a unsigned int into an int and exepect the result to be -1?
我找到了一个 C++ 代码，我们在其中将一个初始化为其最大值的 unsigned int 32 转换为一个 signed int，并期望它是 -1。
它在经过测试的编译器上运行良好，但它真的可以移植吗？
int GetBusinessDataID()
{
u32_t id = ~0;
// Some code that may return a valid ID.
return id; // Here we expect to return -1.
}
自 C++20 以来，integral conversions 保证了这一点；在 C++20 之前，这是实现定义的。
If the destination type is signed, the value does not change if the source integer can be represented in the destination type. Otherwise the result is
implementation-defined (until C++20)
the unique value of the destination type equal to the source value modulo 2n
where n is the number of bits used to represent the destination type. (since C++20).
我找到了一个 C++ 代码，我们在其中将一个初始化为其最大值的 unsigned int 32 转换为一个 signed int，并期望它是 -1。
它在经过测试的编译器上运行良好，但它真的可以移植吗？
int GetBusinessDataID()
{
u32_t id = ~0;
// Some code that may return a valid ID.
return id; // Here we expect to return -1.
}
自 C++20 以来，integral conversions 保证了这一点；在 C++20 之前，这是实现定义的。
If the destination type is signed, the value does not change if the source integer can be represented in the destination type. Otherwise the result is
implementation-defined (until C++20)
the unique value of the destination type equal to the source value modulo 2n where n is the number of bits used to represent the destination type. (since C++20).