Hello, here are the full code demonstrations below:

1. For <iostream> demonstration 1

/*-------------------------------------------------*/

#include <cstdint>
#include <iostream>

int main()
{
    std::int8_t myInt{65};
    std::cout << "Takes ASCII char " << myInt << '\n';
    std::cout << "(static_cast): " << static_cast<int>(myInt) << '\n';
    std::cout << "(int): " << (int)myInt << '\n';

    return 0;
}

// First prints the ASCII character for 65, which is "A"

// (int) and static_cast print 65 correctly.

// The programmer learns to use (int) to print out int8_t

/*-------------------------------------------------*/

2. <iostream> demonstration 2

/*-------------------------------------------------*/

#include <cstdint>
#include <iostream>

int main()
{
    std::cout << "Enter a number between 0 and 127: ";
    std::int8_t myInt{};
    std::cin >> myInt;
    std::cout << "You entered (no cast): " << myInt << '\n';
    std::cout << "You entered (static_cast): " << static_cast<int>(myInt) << '\n';

    std::cout << "You entered ( (int) ): " << (int)myInt << '\n';
    return 0;
}

// *User input:* 35

// You entered: 3                         // this is the first char given onlly. The second one is ignored.

// You entered (static_cast): 51   // this is when the programmer assumes (int) or static_cast<int> should be used

// You entered ( (int )): 51           // 51 is the ASCII number for '3' .

/*-------------------------------------------------*/
3. <cstdio> demonstration 3
/*-------------------------------------------------*/

#include <iostream>
#include <cstdint>
#include <cstdio>
int main()
{
    std::int8_t num{};
    std::scanf("%hhd", &num);                      // Read the number and store it in num
    std::printf("%d this for cstdio.h\n", num); // Print the value of num
    std::cout << sizeof(num) * 8;
    return 0;
}

//*User input*: 100

// prints correctly 100

// size is still int8_t.

On Sat, Dec 23, 2023 at 7:45 AM Yongwei Wu <wuyongwei@gmail.com> wrote:

int8_t is just an alias of signed char, and char, signed char, and unsigned char are all character types (as the names imply). Your first code snippet behaves as expected, as far as the current C++ standard is concerned. I believe you were mistaken somewhere about the second code snippet, and I cannot reproduce what you described.

You might regard the problem as a design defect, but this is a fact already (partly as the price we paid for C compatibility). If one needs an 8-bit integer type that does not behave like a char, a new user-defined type is then needed, as well as some utility functions to support stream input/output. They are quite easy to write (though it is a regret that they do not exist in the standard library).