scanf int8_t corrupts stack - c++

Question

How to scanf int8_t and other types without this error. I used "cinttypes" to get constants of patterns but that didn't help.
#include <cstdio>
#include <cstdint>
#include <cinttypes>
int main()
{
int8_t var;
scanf("%" SCNi8, &var);
printf("%" PRIi8 "\n", var);
return 0;
}
P.S. This error occures only in Debug, when building in Release it's OK.
P.P.S. Output is:
1>------ Build started: Project: SCANF_PROBLEM, Configuration: Debug Win32 ------
1> SCANF_PROBLEM.cpp
1>d:\study\scanf_problem\scanf_problem\scanf_problem.cpp(11): warning C4996: 'scanf': This function or variable may be unsafe. Consider using scanf_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
1> d:\visual studio\vc\include\stdio.h(283) : see declaration of 'scanf'
1> SCANF_PROBLEM.vcxproj -> D:\Study\SCANF_PROBLEM\Debug\SCANF_PROBLEM.exe
========== Build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped ==========

Answer 1

Even in C99, those extended integer types aren't required to exist, unless the documentation says they exist, more on that later... Even if those extended integer types do exist they're not required to have scanf format specifiers. See n1256 section 7.8.1p6 for this quote:
For each type that the implementation provides in <stdint.h>, the corresponding
fprintf macros shall be defined and the corresponding fscanf macros shall be
defined unless the implementation does not have a suitable fscanf length modifier for
the type.
As for C++, well... C++11 delegates that <cstdint> shall essentially be a wrapper for C99s <stdint.h>, and the functions it refers to be wrappers for the C99 equivalents.
Here's the kicker: Microsoft has never cared all that much about C99, to the extent that they're willing to document "N/A" for extended integer support, for example.
Make sure your compiler is configured to compile as C99 or later, or C++11 or later, and link to a C99-or-later-compliant standard library. SCNi8 may exist in the headers, but if scanf doesn't support it (which it won't, prior to C99/C++11 compliance) then you won't have any luck with it... and of course, make sure your standard library documents support for the implementation-defined features you intend to use.
Protip: If your filename ends in .c, Microsoft Visual Studio will attempt to compile your code as C89. That's probably not going to be helpful. MSVC++'s C99-compliance in terms of the standard library isn't too great even when you tell it to compile as C++11. You should probably learn how to determine which compiler/library versions you're using... while you're learning how to compile using the command line.
Protip #2: You can use LLVM/Clang in Visual Studio. Make sure you link to a C99-compliant standard library (e.g. not Microsoft).
Protip #3: You might want to change SCNi8 for PRIi8 when using printf...
Protip #4: See footnote 191 for this quote:
C++ implementations should define these macros only when __STDC_FORMAT_MACROS is defined
before <inttypes.h> is included.

Answer 2

You have run into a bug of Microsoft's C/C++ runtime library, cf. http://mfctips.com/tag/format/ or https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63417 (which reports this bug for gcc under mingw, which links against the Microsft libs).
"%hhd" just doesn't work; you must program around it (which isn't too hard, but sad).
I am not aware of a bug report to MS (i.e., I did not see anything when I tried to google it).