Question

I try to define a 64 bits width integer using C language on Ubnutu 9.10. 9223372036854775808 is 2^23

long long max=9223372036854775808
long max=9223372036854775808

When I compile it, the compiler gave the warning message:

binary.c:79:19: warning: integer constant is so large that it is unsigned
binary.c: In function ‘bitReversal’:
binary.c:79: warning: this decimal constant is unsigned only in ISO C90
binary.c:79: warning: integer constant is too large for ‘long’ type

Is the long type 64 bits width?

Best Regards,

Answer 1

   long long max=9223372036854775808LL; // Note the LL
// long max=9223372036854775808L; // Note the L

---

A long long type is at least 64 bit, a long type is at least 32 bit. Actual width depends on the compiler and targeting platform.

Use int64_t and int32_t to ensure the 64-/32-bit integer can fit into the variable.