64-bit integers in C

[Chaotic42]

Edit: Ok, I'm going to change this instead of making a new thread.

Is there a way to allow access to 64-bit integers in C? I need to manipulate numbers larger than 2147483647.

 

[Armitage]

I had a look. It worked for me with unsigned long int for the type, but not unsigned long long int. What did you figure out?

 

[Chaotic42]

I needed to use %llu instead of %d.

Now I just need to optimize the program.

It's pretty slow.

 

[AgentEL]

which version of C/compiler are you using?

 

[Chaotic42]

GCC 3.3.3 on a dual Athlon system.

 

[AgentEL]

how much larger than 2147483647? unsigned ints can handle twice that.

Edit: Also, declaring a variable as:

long long var = 6000000000;

seems to work as well.

 

[Barnaby W. Füi]

Yep, long long is guaranteed to be at least 64 bits, however you need to make sure and compile your code as c99, not c89/90.

 

[Chaotic42]

Originally posted by: BingBongWongFooey
Yep, long long is guaranteed to be at least 64 bits, however you need to make sure and compile your code as c99, not c89/90.

How do I do that?

 

[glugglug]

__int64 works on most 32-bit compilers.

__int128 works in 64-bit mode. 🙂

 

[Barnaby W. Füi]

Originally posted by: Chaotic42

Originally posted by: BingBongWongFooey
Yep, long long is guaranteed to be at least 64 bits, however you need to make sure and compile your code as c99, not c89/90.

How do I do that?

gcc -std=c99 or -std=gnu99 (c99 w/ gnu extensions)

You could also use a library like glib (guint64 / gint64) or sdl (Uint64 / Sint64), although those might need c99 mode turned on anyways. Not sure.

 

[Barnaby W. Füi]

Or it looks like you can include stdint.h and use int64_t and uint64_t.

http://www.opengroup.org/onlinepubs/009695399/basedefs/stdint.h.html
http://www.delorie.com/gnu/docs/glibc/libc_401.html

 

[Barnaby W. Füi]

Actually stdint.h is part of the c99 standard. 😕

 

[Chaotic42]

Ok, I included stdint.h, compiled with -lm and -std=gnu99, changed the variable type from unsigned long long int to uint_64t, and it still doesn't like numbers larger than 2^31-1.

Here's the top part of the code:

 

[Chaotic42]

I was looking here and it says that unsigned long long int (which I've been using) is 64-bit. I wonder why it's not working for me?

 

[AgentEL]

Originally posted by: Chaotic42
Ok, I included stdint.h, compiled with -lm and -std=gnu99, changed the variable type from unsigned long long int to uint_64t, and it still doesn't like numbers larger than 2^31-1.

Here's the top part of the code:

What do you mean, "it still doesn't like"? Compiler error? Run-time error?

 

[Argo]

Most platforms have int64 datatype defined.

 

[Chaotic42]

Originally posted by: AgentEL

Originally posted by: Chaotic42
Ok, I included stdint.h, compiled with -lm and -std=gnu99, changed the variable type from unsigned long long int to uint_64t, and it still doesn't like numbers larger than 2^31-1.

Here's the top part of the code:

What do you mean, "it still doesn't like"? Compiler error? Run-time error?

I mean it caps the numbers at 2^31-1.

If I put in 999999999999999999999999999999 it caps it at 2147483647.

 

[EmperorRob]

Are you using literal numbers in your assignments? They need the LLU(or maybe it's ULL) identifier on the end or they automatically get converted to another datatype (ints I think).

Like this

unsigned long long int total = 99999999999999ULL + 8888888888888ULL

 

[Chaotic42]

I have them read in from the command line. Is there anything I can do for those?

 

[Barnaby W. Füi]

strtoll() ?

 

[ivan2]

http://p2p.wrox.com/post.asp?method=ReplyQuote&REPLY_ID=39703&TOPIC_ID=17013&FORUM_ID=83

gcc has data type "long long" for 64-bit integers, "%lld" is the conversion specifier for scanf/printf functions

 

[EmperorRob]

That would be a good way to do it in C.

The way that I've seen recommended for C++ is to use stringstream 's:

http://www.parashift.com/c++-faq-lite/misc-technical-issues.html#faq-38.2