Question

I’m trying to use 64 bit integers in C, but am getting mixed signals as to whether it should be possible.

When I execute the printf:

printf("Size of long int:%d\nSize of long long int:%d\n\n",(int)sizeof(long int), (int)sizeof(long long int));

The response I get is:

Size of long int:4
Size of long long int:8

This makes me feel that a long long int has 8 bytes = 64 bits.

However, when I try to declare the following variables:

long long int a2 = 0x00004444;
long long int b2 = 0x000044440;
long long int c2 = 0x0000444400;
long long int d2 = 0x00004444000;
long long int e2 = 0x000044440000;
long long int f2 = 0x0000444400004;
long long int g2 = 0x00004444000044;
long long int h2 = 0x000044440000444;
long long int i2 = 0x0000444400004444;

The last 4 variables (f2,g2,h2,i2) give me the error message:

warning: integer constant is too large for ‘long’ type

I get the same result when I replace ‘long long int’ with ‘int64_t’. I assume ‘int64_t’ was recognized, since it didn’t generate any error messages of its own.

So, it appears my 8 byte long long int is really a 6 byte long long int, and I don’t understand what I’m missing here. If it’s any help, here is the information on my gcc compiler:

me@ubuntu:~$ gcc -v  
Using built-in specs.  
Target: i686-linux-gnu  
Configured with: ../src/configure -v   
--with-pkgversion='Ubuntu/Linaro 4.4.4-14ubuntu5'  
--with-bugurl=file:///usr/share/doc/gcc-4.4/README.Bugs   
--enable-languages=c,c++,fortran,objc,obj-c++  
--prefix=/usr   
--program-suffix=-4.4   
--enable-shared   
--enable-multiarch   
--enable-linker-build-id   
--with-system-zlib   
--libexecdir=/usr/lib   
--without-included-gettext   
--enable-threads=posix   
--with-gxx-include-dir=/usr/include/c++/4.4   
--libdir=/usr/lib   
--enable-nls   
--with-sysroot=/ -  
-enable-clocale=gnu   
--enable-libstdcxx-debug   
--enable-objc-gc   
--enable-targets=all 
--disable-werror   
--with-arch-32=i686   
--with-tune=generic   
--enable-checking=release   
--build=i686-linux-gnu   
--host=i686-linux-gnu   
--target=i686-linux-gnu  
Thread model: posix  
gcc version 4.4.5 (Ubuntu/Linaro 4.4.4-14ubuntu5)   

If anyone knows how (or if) 64 bit integers are accessible to me, I’d really appreciate any help. Thanks….

Answer 1

Use stdint.h for specific sizes of integer data types, and also use appropriate suffixes for integer literal constants, e.g.:

#include <stdint.h>

int64_t i2 = 0x0000444400004444LL;