Programming in C

5.0 Expressions 447

5.11 sizeofOperator

Given that

type is as described previously;

a is an expression;

then the expression

sizeof (type) has as its value the number of bytes needed to contain a value of

the specified type;

sizeof a has as its value the number of bytes required to hold the result

of the evaluation of a.

If typeis char, the result is defined to be 1. If ais the name of an array that has been

dimensioned (either explicitly or implicitly through initialization) and is not a formal

parameter or undimensioned externarray,sizeof agives the number of bytes required

to store the elements in a.

The type of integer produced by the sizeofoperator is size_t, which is defined in

the standard header file <stddef.h>.

If ais a variable-length array, the sizeofoperator is evaluated at runtime; otherwise a

is evaluated at compile time and the result can be used in constant expressions (see

Section 5.2).

5.12 Comma Operator

Given that

a, b are expressions;

then the expression

a, b causes ato be evaluated and then bto be evaluated; the type and value

of the expression is that of b.

5.13 Basic Operations with Arrays

Given that

a is declared as an array of nelements;

i is an expression of any integer data type;

v is an expression;

then the expression

a[0] references the first element of a;

a[n - 1] references the last element of a;

a[i] references element number iof a;

a[i] = v stores the value of vinto a[i].

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