_Countof (Using the GNU Compiler Collection (GCC))

#### 6.12.6 Determining the Number of Elements of Arrays ¶

The keyword `_Countof` determines the number of elements of an array operand. Its syntax is similar to `sizeof`. The operand must be a parenthesized complete array type name or an expression of such a type. For example:

    int a[n];
    _Countof (a);  // returns n
    _Countof (int [7][3]);  // returns 7

The result of this operator is an integer constant expression, unless the array has a variable number of elements. The operand is only evaluated if the array has a variable number of elements. For example:

    _Countof (int [7][n++]);  // integer constant expression
    _Countof (int [n++][7]);  // run-time value; n++ is evaluated