Why "auto x = -2147483648;" sets x to unsigned long type not to int type? (VS2017)

Question

auto x = -2147483648; // (unsigned long)
auto y = -2147483647; // (int)

In C language, the range of int type is "-2,147,483,648 ~ 2,147,483,647".

I think -2147483648 can be represented as an int type but represented as an unsigned long. Furthermore -2147483648 is out of range of the unsigned long type.

Why...?

(I'm using Visual Studio 2017)

Edited!

Wow. I read comments and I realized that my question should have been more precise.

1) Yes, In C++ language not in C language. (sorry)

2) int type range? : https://msdn.microsoft.com/en-us/library/s3f49ktz.aspx

INT_MIN is define in limits.h

//
// limits.h
//
//      Copyright (c) Microsoft Corporation. All rights reserved.
//
// The C Standard Library <limits.h> header.
//

#define SHRT_MIN    (-32768)        // minimum (signed) short value
#define SHRT_MAX      32767         // maximum (signed) short value
#define USHRT_MAX     0xffff        // maximum unsigned short value
#define INT_MIN     (-2147483647 - 1) // minimum (signed) int value
#define INT_MAX       2147483647    // maximum (signed) int value
#define UINT_MAX      0xffffffff    // maximum unsigned int value
#define LONG_MIN    (-2147483647L - 1) // minimum (signed) long value
#define LONG_MAX      2147483647L   // maximum (signed) long value
#define ULONG_MAX     0xffffffffUL  // maximum unsigned long value
#define LLONG_MAX     9223372036854775807i64       // maximum signed long long int value
#define LLONG_MIN   (-9223372036854775807i64 - 1)  // minimum signed long long int value
#define ULLONG_MAX    0xffffffffffffffffui64       // maximum unsigned long long int value

Fun fact for you `-2147483648` is not an integer constant. `2147483648` is one, and `-` is applied to it. — StoryTeller - Unslander Monica, Nov 08 '17 at 06:18
@NickyC - Nope. The OP obviously built as C++, but didn't know it was C++. — StoryTeller - Unslander Monica, Nov 08 '17 at 06:19
@NickyC In C, `auto x` same as `auto int x`. `auto` represents an automatic variable. (So not `static`) — BLUEPIXY, Nov 08 '17 at 06:21
@BLUEPIXY - It's just ill-formed in C99 an onward. One should build with ISO compliance. There is no implicit int in C anymore. — StoryTeller - Unslander Monica, Nov 08 '17 at 06:22
So, the OP posts C++ code, talks about auto type deduction, and calls it C language? — , Nov 08 '17 at 06:23
@NickyC - Pretty much, yeah. But since they are using Visual Studio I think we can excuse them. Microsoft don't want to support C properly. — StoryTeller - Unslander Monica, Nov 08 '17 at 06:25
@4386427 I know what `auto` keyword does in modern and old C and C++. You don't need to throw the standard at me. I know where to look them up. My concern is the question is getting unclear, we are getting many speculations and may be all wrong, and the OP does not come out and clarify. — , Nov 08 '17 at 06:33
@NickyC - If the OP just drops a question and doesn't hang around for a couple of minutes to clarify any queries (and we brought up our concerns very fast), then we should just downvote and carry on with our day. The post has earned it. — StoryTeller - Unslander Monica, Nov 08 '17 at 06:37

score 0 · Answer 1 · answered Nov 08 '17 at 07:12

There is no automatic type deduction in C. Lone auto without type specifiers either means auto int or is ill-formed, depending on what vintage of the C standard you are talking about. The implicit int feature was removed from the language in 1999.

Sample 1

Sample 2

If your tools are telling you that x is of type unsigned long, they are either buggy or set up for a language other than C (or both).

Note, this answer was written when the question was tagged with the C tag and didn't mention C++.

score -2 · Accepted Answer · answered Nov 09 '17 at 05:47

-2

I found the answer.

Why does the smallest int, −2147483648, have type 'long'?

The answer explains that -2147483648 is same to -(2147483648).

answered Nov 09 '17 at 05:47

wonsch

37
8

Why "auto x = -2147483648;" sets x to unsigned long type not to int type? (VS2017)

Edited!

2 Answers2