C Type Specifiers
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The latest version of this topic can be found at C Type Specifiers.
Type specifiers in declarations define the type of a variable or function declaration.
Syntax
type-specifier:
void
char
short
int
long
float
double
signed
unsigned
struct-or-union-specifier
enum-specifier
typedef-name
The signed char, signed int, signed short int, and signed long int types, together with their unsigned counterparts and enum, are called "integral" types. The float, double, and long double type specifiers are referred to as "floating" or "floating-point" types. You can use any integral or floating-point type specifier in a variable or function declaration. If a type-specifier is not provided in a declaration, it is taken to be int.
The optional keywords signed and unsigned can precede or follow any of the integral types, except enum, and can also be used alone as type specifiers, in which case they are understood as signed int and unsigned int, respectively. When used alone, the keyword int is assumed to be signed. When used alone, the keywords long and short are understood as long int and short int.
Enumeration types are considered basic types. Type specifiers for enumeration types are discussed in Enumeration Declarations.
The keyword void has three uses: to specify a function return type, to specify an argument-type list for a function that takes no arguments, and to specify a pointer to an unspecified type. You can use the void type to declare functions that return no value or to declare a pointer to an unspecified type. See Arguments for information on void when it appears alone within the parentheses following a function name.
Microsoft Specific
Type checking is now ANSI-compliant, which means that type short and type int are distinct types. For example, this is a redefinition in the Microsoft C compiler that was accepted by previous versions of the compiler.
int myfunc();
short myfunc();
This next example also generates a warning about indirection to different types:
int *pi;
short *ps;
ps = pi; /* Now generates warning */
The Microsoft C compiler also generates warnings for differences in sign. For example:
signed int *pi;
unsigned int *pu
pi = pu; /* Now generates warning */
Type void expressions are evaluated for side effects. You cannot use the (nonexistent) value of an expression that has type void in any way, nor can you convert a void expression (by implicit or explicit conversion) to any type except void. If you do use an expression of any other type in a context where a void expression is required, its value is discarded.
To conform to the ANSI specification, void** cannot be used as int**. Only void* can be used as a pointer to an unspecified type.
END Microsoft Specific
You can create additional type specifiers with typedef declarations, as described in Typedef Declarations. See Storage of Basic Types for information on the size of each type.