Constants and sizeof
beginner9 min readLesson 6 of 148
Values that cannot change (const, #define) and asking the compiler how big things really are.
Constants
A const variable cannot be assigned after initialization:
const int MAX_USERS = 100;
MAX_USERS = 5; // compile error
#define is a preprocessor text substitution — different mechanism, same goal
for simple constants:
#define MAX_USERS 100 // no semicolon, no equals
Prefer const for typed constants; you will meet the preprocessor properly in
module 17.
sizeof asks the compiler
sizeof yields the size of a type or expression in bytes; its result type
is size_t, printed with %zu:
printf("%zu\n", sizeof(int)); // typically 4
printf("%zu\n", sizeof(double)); // typically 8
char c = 'x';
printf("%zu\n", sizeof(c)); // 1
sizeof is evaluated at compile time for types — no runtime cost.