Console not reading input string correctly

I tried to read a console input by executing C++-style

int main()
{
    std::string str;
    std::getline(std::cin, str);
    // also tested: std::cin >> str;
    return 0;
}

and C-style

int main()
{
    char* str = new char[20];
    scanf_s("%s", str);
    delete[] str;
    return 0;
}

But if I enter a string and press enter, the cursor in console won't jump to the next line, it jumps to the first column of the line where the entered command is located. A second key down on enter will cause an error:

Error message box after executing C++-style code:

Debug Assertion Failed!

Program: D:\_extern\Test\Test.exe
File: minkernel\crts\ucrt\src\appcrt\lowio\read.cpp
Line: 259

Expression: static_cast<void const*>(source_buffer) == static_cast<void const*>(result_buffer)

For information on how your program can cause an assertion
failure, see the Visual C++ documentation on asserts.

Error after executing C-style code:

Exception triggered at 0x00007FF95C9398E9 (ucrtbased.dll) in Test.exe: 0xC0000005: Access violation when writing at position 0x0000019155DF1000.

What could be the problem?

You're not calling scanf_s() correctly, you're calling it as if it were ordinary scanf(). From the documentation:

Unlike scanf and wscanf, scanf_s and wscanf_s require the buffer size to be specified for all input parameters of type c, C, s, S, or string control sets that are enclosed in []. The buffer size in characters is passed as an additional parameter immediately following the pointer to the buffer or variable. For example, if you are reading a string, the buffer size for that string is passed as follows:

char s[10];
scanf_s("%9s", s, (unsigned)_countof(s)); // buffer size is 10, width specification is 9

So in your case, you need to write:

scanf_s("%s", str, 20);