Chapter 22: Variable Declaration Keywords

int& r = x; // error

struct S { void f();

void g() const;

};

const S s; s.f(); // error s.g(); // OK

Section 22.3: volatile

A type qualifier; when applied to a type, produces the volatile-qualified version of the type. Volatile qualification plays the same role as const qualification in the type system, but volatile does not prevent objects from being modified; instead, it forces the compiler to treat all accesses to such objects as side e ects.

In the example below, if memory_mapped_port were not volatile, the compiler could optimize the function so that it performs only the final write, which would be incorrect if sizeof(int) is greater than 1. The volatile qualification forces it to treat all sizeof(int) writes as di erent side e ects and hence perform all of them (in order).

extern volatile char memory_mapped_port; void write_to_device(int x) {

const char* p = reinterpret_cast<const char*>(&x); for (int i = 0; i < sizeof(int); i++) {

memory_mapped_port = p[i];

}

}

Section 22.4: signed

A keyword that is part of certain integer type names.

When used alone, int is implied, so that signed, signed int, and int are the same type.

When combined with char, yields the type signed char, which is a di erent type from char, even if char is also signed. signed char has a range that includes at least -127 to +127, inclusive.

When combined with short, long, or long long, it is redundant, since those types are already signed.

signed cannot be combined with bool, wchar_t, char16_t, or char32_t.

Example:

signed char celsius_temperature; std::cin >> celsius_temperature; if (celsius_temperature < -35) {

std::cout << "cold day, eh?\n";

}

Section 22.5: unsigned

A type specifier that requests the unsigned version of an integer type.

When used alone, int is implied, so unsigned is the same type as unsigned int.

The type unsigned char is di erent from the type char, even if char is unsigned. It can hold integers up to at least 255.

unsigned can also be combined with short, long, or long long. It cannot be combined with bool, wchar_t, char16_t, or char32_t.