Should I use static_cast or INT64_C to assign 64-bit constant portably?

Question

Assigning a 64-bit constant as

int64_t foo = 0x1234LL;

is not portable, because long long isn't necessarily int64_t. This post Which initializer is appropriate for an int64_t? discusses use of INT64_C() macro from <stdint.h>, but isn't it also possible to use static_cast as

int64_t foo = static_cast<int64_t>(0x1234);

?

Which one should I prefer and why, or do both of them work well?

I have searched on the internet and on SO, but did not find any place where the static_cast option is explored. I have also done tests using sizeof() to confirm that it works in the simple cases.

Answer 1

Actually, long long is guaranteed to be at least 64 bits by the C implementation limits header <climits>. The minimum limit on the minimum and maximum values for an object of type long long is given as:

LLONG_MIN   -9223372036854775807 // −(2^63 − 1)
LLONG_MAX   +9223372036854775807 // 2^63 − 1

This corresponds to a signed 64 bit integer. You cannot store such a range of values without at least 64 information bits.

So go ahead and use 0x1234LL. In fact, you can just as much use no suffix, because the first of the following types that can fit the value will be chosen:

Suffix | Decimal constants | Octal or hexadecimal constant
-------|-------------------|------------------------------
none   | int               | int
       | long int          | unsigned int
       | long long int     | long int
       |                   | unsigned long int
       |                   | long long int
       |                   | unsigned long long int
...    | ...               | ...