int64_t == long long

int64_t == long long

[Yang Zhang]

Hi, why isn't int64_t == long long at least on 64-bit x86 Linux?

http://gcc.gnu.org/onlinedocs/gcc-3.3.6/gcc/Long-Long.html

says that these are *at least* 64 bits.  How do I tell what type this 
actually is?  And are literals ending with LL always long long?

Thanks in advance for any answers!



$ uname -a
Linux yang-xps410 2.6.24-19-generic #1 SMP Wed Jun 18 14:15:37 UTC 2008 
x86_64 GNU/Linux

$ cat longlongint.cc
#include <iostream>
#include <string>

using namespace std;

void f(int64_t x) { cout << x << endl; }
void f(int32_t x) { cout << x << endl; }
void f(int16_t x) { cout << x << endl; }
void f(int8_t  x) { cout << x << endl; }
void f(double  x) { cout << x << endl; }
void f(float   x) { cout << x << endl; }
void f(string& x) { cout << x << endl; }

int
main()
{
   long long int x = 32;
   f(x);
   int64_t y = 32;
   f(y);
   f(0LL);
   return 0;
}

$ g++ -pedantic -Wall -Wextra longlongint.cc
longlongint.cc:21:5: warning: use of C99 long long integer constant
longlongint.cc: In function âint main()â:
longlongint.cc:17: error: ISO C++ does not support âlong longâ
longlongint.cc:18: error: call of overloaded âf(long long int&)â is 
ambiguous
longlongint.cc:6: note: candidates are: void f(int64_t)
longlongint.cc:7: note:                 void f(int32_t)
longlongint.cc:8: note:                 void f(int16_t)
longlongint.cc:9: note:                 void f(int8_t)
longlongint.cc:10: note:                 void f(double)
longlongint.cc:11: note:                 void f(float)
longlongint.cc:21: error: call of overloaded âf(long long int)â is ambiguous
longlongint.cc:6: note: candidates are: void f(int64_t)
longlongint.cc:7: note:                 void f(int32_t)
longlongint.cc:8: note:                 void f(int16_t)
longlongint.cc:9: note:                 void f(int8_t)
longlongint.cc:10: note:                 void f(double)
longlongint.cc:11: note:                 void f(float)

-- 
Yang Zhang
http://www.mit.edu/~y_z/

Re: int64_t == long long

[John Love-Jensen]

On 7/1/08 2:17 PM, "Yang Zhang" <yanghatespam@gmail.com> wrote:

> Hi, why isn't int64_t == long long at least on 64-bit x86 Linux?

Because int64_t should be 64-bit, but long long could be 64-bit or larger.

#include <stdint.h> // from C99
#include <climits>

cout << (sizeof(int64_t) * CHAR_BIT) << endl;
cout << (sizeof(long long) * CHAR_BIT) << endl;

You can also do this:

#include <stdint.h> // from C99
#include <typeinfo>

cout << typeid(int64_t).name() << endl;
cout << typeid(long long).name() << endl;

> How do I tell what type this actually is?

typeid

> And are literals ending with LL always long long?

Yes, that's what the LL suffix means.

So the literal integer numerics are:
'A'
L'A'
65
65L
65LL
65U
65UL
65ULL

Keep in mind the portability issues surrounding use of long long, LL, and
ULL.  You may want to use the <stdint.h> INT64_C and UINT64_C macros to
construct your numeric literals.

INT64_C(65)
UINT64_C(65)

HTH,
--Eljay

Re: int64_t == long long

[Yang Zhang]

John Love-Jensen wrote:
> On 7/1/08 2:17 PM, "Yang Zhang" <yanghatespam@gmail.com> wrote:
> 
>> Hi, why isn't int64_t == long long at least on 64-bit x86 Linux?
> 
> Because int64_t should be 64-bit, but long long could be 64-bit or larger.
> 
> #include <stdint.h> // from C99
> #include <climits>
> 
> cout << (sizeof(int64_t) * CHAR_BIT) << endl;
> cout << (sizeof(long long) * CHAR_BIT) << endl;

   cout << sizeof(int64_t) << endl;
   cout << sizeof(long long) << endl;

print:

8
8

> 
> You can also do this:
> 
> #include <stdint.h> // from C99
> #include <typeinfo>
> 
> cout << typeid(int64_t).name() << endl;
> cout << typeid(long long).name() << endl;

This prints:

l
x

What does this mean?  (typeid(string).name() prints "Ss")

-- 
Yang Zhang
http://www.mit.edu/~y_z/

Re: int64_t == long long

[Wesley Smith]

>  cout << sizeof(int64_t) << endl;
>  cout << sizeof(long long) << endl;
>
> print:
>
> 8
> 8


8*8 = 64

sizeof reports the # of bytes, not bits.
wes

Re: int64_t == long long

[Yang Zhang]

Wesley Smith wrote:
>>  cout << sizeof(int64_t) << endl;
>>  cout << sizeof(long long) << endl;
>>
>> print:
>>
>> 8
>> 8
> 
> 
> 8*8 = 64
> 
> sizeof reports the # of bytes, not bits.
> wes

Thanks, I knew that.  I was just confused why they weren't then being 
treated as the same type.

-- 
Yang Zhang
http://www.mit.edu/~y_z/

Re: int64_t == long long

[John Love-Jensen]

Hi Yang Zhang,

>> cout << typeid(int64_t).name() << endl;
>> cout << typeid(long long).name() << endl;
> 
> This prints:
> 
> l
> x
> 
> What does this mean?

This means that they are not the same type.

HTH,
--Eljay

Re: int64_t == long long

[Yang Zhang]

John Love-Jensen wrote:
> Hi Yang Zhang,
> 
>>> cout << typeid(int64_t).name() << endl;
>>> cout << typeid(long long).name() << endl;
>> This prints:
>>
>> l
>> x
>>
>> What does this mean?
> 
> This means that they are not the same type.
> 
> HTH,
> --Eljay
> 

You're right, of course, and I knew they were different already, without 
needing to see the above output.  I just wasn't sure if that was the 
correct/expected output (I was assuming I'd get a more human-friendly name).

Steering this thread back on track: I'm still not sure why these are 
different.  So far, I know that both long long and int64_t are 64-bit 
signed integral types.  They still don't have to actually be the same 
type, but I was hoping someone would be able to explain things to a bit 
more depth (e.g. rationale).
-- 
Yang Zhang
http://www.mit.edu/~y_z/

Re: int64_t == long long

[John Love-Jensen]

Hi Yang Zhang,

My guess (purely speculative, not authoritative) is that on your platform, a
long int is 64-bit, and a long long is 64-bit.  Assuming that guess is
correct, since long int is 64-bit *AND* long int is part of the C99 standard
the stdint.h used long int to be the alias for int64_t.  Whereas long long
is a compiler extension*, so the long int was preferential to long long.

Sincerely,
--Eljay

* Is long long still a compiler extension for C99?  I don't use C99.

Re: int64_t == long long

[Yang Zhang]

John Love-Jensen wrote:
> Hi Yang Zhang,
> 
> My guess (purely speculative, not authoritative) is that on your platform, a
> long int is 64-bit, and a long long is 64-bit.  Assuming that guess is
> correct, since long int is 64-bit *AND* long int is part of the C99 standard
> the stdint.h used long int to be the alias for int64_t.  Whereas long long
> is a compiler extension*, so the long int was preferential to long long.
> 
> Sincerely,
> --Eljay
> 
> * Is long long still a compiler extension for C99?  I don't use C99.
> 

Hmm, you're right.  So far, I believe:

On 64-bit:
   ??????? == long long int, aka long long
   int64_t == long int, aka long
   int32_t == int

On 32-bit:
   int64_t == long long int, aka long long
   int32_t == long int, aka long
   int32_t == int

The mystery deepens.

(And I don't know about the C99 story.)

-- 
Yang Zhang
http://www.mit.edu/~y_z/

Re: int64_t == long long

[Yang Zhang]

John Love-Jensen wrote:
> Keep in mind the portability issues surrounding use of long long, LL, and
> ULL.  You may want to use the <stdint.h> INT64_C and UINT64_C macros to
> construct your numeric literals.
> 
> INT64_C(65)
> UINT64_C(65)

I'm using gcc 4.2.3 and this doesn't compile (INT64_C doesn't exist).

#include <stdint.h>
#include <stdio.h> 


int
main()
{
   printf("%lld\n", INT64_C(0));
   return 0;
}

-- 
Yang Zhang
http://www.mit.edu/~y_z/

Re: int64_t == long long

[Philipp Thomas]

* Yang Zhang (yanghatespam@gmail.com) [20080702 06:50]:

> Steering this thread back on track: I'm still not sure why these are 
> different.  So far, I know that both long long and int64_t are 64-bit 
> signed integral types.

int64_t is a typedef, *not* a base type. The actual type depends on the
platform. For i386, int64_t is a typedef for long long, on an LP64 arch as
x86-64, it's a typedef for long as longs are 64 bits.

> but I was hoping someone would be able to explain things to a bit more 
> depth (e.g. rationale).

Does the above make it clearer?

Philipp