ISO C99 and ISO C++11 support data types for integers that are at least 64 bits wide, and as an extension GCC supports them in C90 and C++98 modes. Simply write
long long int for a signed integer, or
unsigned long long int for an unsigned integer. To make an integer constant of type
long long int, add the suffix ‘LL’ to the integer. To make an integer constant of type
unsigned long long int, add the suffix ‘ULL’ to the integer.
You can use these types in arithmetic like any other integer types. Addition, subtraction, and bitwise boolean operations on these types are open-coded on all types of machines. Multiplication is open-coded if the machine supports a fullword-to-doubleword widening multiply instruction. Division and shifts are open-coded only on machines that provide special support. The operations that are not open-coded use special library routines that come with GCC.
There may be pitfalls when you use
long long types for function arguments without function prototypes. If a function expects type
int for its argument, and you pass a value of type
long long int, confusion results because the caller and the subroutine disagree about the number of bytes for the argument. Likewise, if the function expects
long long int and you pass
int. The best way to avoid such problems is to use prototypes.