Simple Types

Overview

The bottom of the type hierarchy consists of simple types. This comprises the primitive types that all other types are either based off of or derived from.

Signed	Unsigned	32-bit	64-bit
-	bool	1	1
signed char	unsigned char	1	1
short	unsigned short	2	2
int	unsigned	4	4
long	unsigned long	4	8
long long	unsigned long long	8	8

Real	Complex	32-bit	64-bit
float	-	4	4
double	-	8	8
long double	-	-	-
-	float complex	4	4
-	double complex	8	8
-	long double complex	-	-

Integers

Narrow types cannot be used directly in arithmetic. Instead they are first promoted to a wider type. On almost every system, this promotion will be to a signed int of the same value, regardless of the signedness of the narrow type itself.

Character Types

The three types char, signed char, and unsigned char are collectively called the character types. The implementation defines char to have the same range, representation, and behavior as either signed char or unsigned char, but is considered incompatible with both. That is, it is a distinct type in the eyes of the type system.

Unsigned Integers

Name	Narrow	Rank	Minimum Width
bool	Yes	0	1
char (maybe)	Yes	1	-
unsigned char	Yes	1	8
unsighed short	Yes	2	16
unsigned int	No	3	16
unsigned long	No	4	32
unsigned long long	No	5	64

Signed Integers

Name	Narrow	Rank	Minimum Width
char (maybe)	Yes	1	-
signed char	Yes	1	8
signed short	Yes	2	16
signed int	No	3	16
signed long	No	4	32
signed long long	No	5	64
float	-	-	-
double	-	-	-
long double	-	-	-

Literals

Negative integer literals are typed in a counterintuitive way. When the compiler sees a number of form -X, the type of X is determined before being negated. Promotion follows the first fit rule described as follows:

Decimal	Oct/Hex
int	int
long	unsigned
long long	long
-	unsigned long
-	long long
-	unsigned long long

Integer constants can be made a certain signedness or type by using the following suffixes:

Suffix	Type
U	unsigned
L	long
LL	long long
ULL	unsigned long long

Integer Constant Expressions

An integer constant expression (ICE) is a compile-time integer value. Its value must be determinable at compile time (e.g. no function calls are permitted), and also no evaluation of an object must participate as an operand.

Floating Point

Literals

Floating-point constants can be made a certain type by using the following suffixes:

Suffix	Type
F	float
L	long double

Exact-Width Integer Types

The stdint.h library contains exact-width integer types. These are aliases to types that represent an exact width and sign representation:

• If the type uintN_t is provided, it is an unsigned integer type with exactly $N$ bits of width and precision.
• If the type intN_t is provided, is is signed, with two’s complement representation, has a width of exactly $N$ bits and a precision of $N-1$.

The C standard says these typedefs must be defined if they can be satisfied. Otherwise they may not exist.

Enumerated Types

An enum is a mapping of identifiers with integer values. They have general form:

enum optional_tag {
  type1 ident1;
  ...
  typeN identN;
} optional_var1 ... optional_varN;

Bibliography

• “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.
• Jens Gustedt, Modern C (Shelter Island, NY: Manning Publications Co, 2020).
• Raymond, Eric. “The Lost Art of Structure Packing.” Accessed November 4, 2024. http://www.catb.org/esr/structure-packing/.
• Van der Linden, Peter. Expert C Programming: Deep C Secrets. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.