Menu
I'm a tad confused between what is and is not a Constant Expression in C, even after much Googleing. Could you provide an example of something which is, and which is not, a Constant Expression in C?
935
Moreover, in C language, the term "constant" refers to literal constants (like 1 , 'a' , 0xFF and so on), enum members, and results of such operators as sizeof . Const-qualified objects (of any type) are not constants in C language terminology.
A constant is a value or variable that can't be changed in the program, for example: 10, 20, 'a', 3.4, "c programming" etc.
A constant expression gets evaluated at compile time, not run time, and can be used in any place that a constant can be used. The constant expression must evaluate to a constant that is in the range of representable values for that type.
Primary constants − Integer, float, and character are called as Primary constants. Secondary constants − Array, structures, pointers, Enum, etc., called as secondary constants.
A constant expression can be evaluated at compile time. That means it has no variables in it. For example:
5 + 7 / 3
is a constant expression. Something like:
5 + someNumber / 3
is not, assuming someNumber is a variable (ie, not itself a compile-time constant).
117
Nobody seems have mentioned yet another kind of constant expression: address constants. The address of an object with static storage duration is an address constant, hence you can do this kind of thing at file scope:
char x;
char *p = &x;
String literals define arrays with static storage duration, so this rule is also why you can do this at file scope:
char *s = "foobar";
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
