C++ 为什么数值限制对 uint8_t 和 int8_t 不起作用？

Question

我最近注意到 numeric_limits::max() 和 numeric_limits::min() 似乎不适用于 uint8_t 和 int8_t。这是有原因的还是可能是错误？我在自己的电脑上尝试使用 gcc 编译器：

#include <iostream>
#include <limits>

using namespace std;

int main()
{

    std::cout << "numeric_limits<uint8_t>::max() = " << numeric_limits<uint8_t>::max() << std::endl; 
    std::cout << "numeric_limits<int8_t>::max() = " << numeric_limits<int8_t>::max() << std::endl; 
    std::cout << "numeric_limits<int8_t>::min() = " << numeric_limits<int8_t>::min() << std::endl;

    std::cout << "numeric_limits<uint16_t>::max() = " << numeric_limits<uint16_t>::max() << std::endl; 
    std::cout << "numeric_limits<int16_t>::max() = " << numeric_limits<int16_t>::max() << std::endl; 
    std::cout << "numeric_limits<int16_t>::min() = " << numeric_limits<int16_t>::min() << std::endl; 

    std::cout << "numeric_limits<uint32_t>::max() = " << numeric_limits<uint32_t>::max() << std::endl; 
    std::cout << "numeric_limits<int32_t>::max() = " << numeric_limits<int32_t>::max() << std::endl; 
    std::cout << "numeric_limits<int32_t>::min() = " << numeric_limits<int32_t>::min() << std::endl; 

    std::cout << "numeric_limits<uint64_t>::max() = " << numeric_limits<uint64_t>::max() << std::endl; 
    std::cout << "numeric_limits<int64_t>::max() = " << numeric_limits<int64_t>::max() << std::endl; 
    std::cout << "numeric_limits<int64_t>::min() = " << numeric_limits<int64_t>::min() << std::endl; 

    return 0;
}

给出输出：

numeric_limits<uint8_t>::max() = �
numeric_limits<int8_t>::max() = 
numeric_limits<int8_t>::min() = �
numeric_limits<uint16_t>::max() = 65535
numeric_limits<int16_t>::max() = 32767
numeric_limits<int16_t>::min() = -32768
numeric_limits<uint32_t>::max() = 4294967295
numeric_limits<int32_t>::max() = 2147483647
numeric_limits<int32_t>::min() = -2147483648
numeric_limits<uint64_t>::max() = 18446744073709551615
numeric_limits<int64_t>::max() = 9223372036854775807
numeric_limits<int64_t>::min() = -9223372036854775808

Answer 1

确实有效。虽然输出被解释为 ASCII 字符。如果在打印前转换为 int，您将看到正确的值：

std::cout << "numeric_limits<uint8_t>::max() = " << static_cast<int>(numeric_limits<uint8_t>::max()) << std::endl; 
std::cout << "numeric_limits<int8_t>::max() = " << static_cast<int>(numeric_limits<int8_t>::max()) << std::endl; 
std::cout << "numeric_limits<int8_t>::min() = " << static_cast<int>(numeric_limits<int8_t>::min()) << std::endl;

Answer 2

int8 类型可能定义为 chars，因此不要将值打印为 char，而是打印为 ints:

int main() {

    std::cout << "numeric_limits<uint8_t>::max() = " << (int)numeric_limits<uint8_t>::max() << std::endl; 
    std::cout << "numeric_limits<int8_t>::max() = " << (int)numeric_limits<int8_t>::max() << std::endl; 
    std::cout << "numeric_limits<int8_t>::min() = " << (int)numeric_limits<int8_t>::min() << std::endl;
}

Answer 3

std::cout << "numeric_limits<uint8_t>::max() = " << std::to_string(numeric_limits<uint8_t>::max()) << std::endl; 
std::cout << "numeric_limits<int8_t>::max() = " << std::to_string(numeric_limits<int8_t>::max()) << std::endl; 
std::cout << "numeric_limits<int8_t>::min() = " << std::to_string(numeric_limits<int8_t>::min()) << std::endl;

尝试将它们转换为字符串，然后再将它们插入 cout。

C++ 为什么数值限制对 uint8_t 和 int8_t 不起作用？

C++ Why numeric limits doesn't work for uint8_t and int8_t?

c++

numeric-limits