Arithmetic types

(See also type for type system overview and the list of type-related utilities that are provided by the C library).

Character types

• signed char - type for signed character representation.
• unsigned char - type for unsigned character representation. Also used to inspect object representations (raw memory).
• char - type for character representation. Equivalent to either signed char or unsigned char (which one is implementation-defined and may be controlled by a compiler commandline switch), but char is a distinct type, different from both signed char both unsigned char

Note that the standard library also defines typedef names wchar_t , char16_t, and char32_t (since C11) to represent wide characters.

Integer types

• short int (also accessible as short, may use the keyword signed)
• unsigned short int (also accessible as unsigned short)
• int (also accessible as signed int)
• unsigned int (also accessible as unsigned), the unsigned counterpart of int, implementing modulo arithmetic. Suitable for bit manipulations.
• long int (also accessible as long)
• unsigned long int (also accessible as unsigned long)

Note: as with all type specifiers, any order is permitted: unsigned long long int and long int unsigned long name the same type.

The following table summarizes all available integer types and their properties:

Besides the minimal bit counts, the C Standard guarantees that 1 == sizeof(char) <= sizeof(short) <= sizeof(int) <= sizeof(long) <= sizeof(long long).

Note: this allows the extreme case in which bytes are sized 64 bits, all types (including char) are 64 bits wide, and sizeof returns 1 for every type.

Note: integer arithmetic is defined differently for the signed and unsigned integer types. See arithmetic operators, in particular integer overflows.

Data models

The choices made by each implementation about the sizes of the fundamental types are collectively known as data model. Four data models found wide acceptance:

32 bit systems:

• LP32 or 2/4/4 (int is 16-bit, long and pointer are 32-bit)
• Win16 API
• ILP32 or 4/4/4 (int, long, and pointer are 32-bit);
• Win32 API
• Unix and Unix-like systems (Linux, Mac OS X)

64 bit systems:

• LLP64 or 4/4/8 (int and long are 32-bit, pointer is 64-bit)
• Win64 API
• LP64 or 4/8/8 (int is 32-bit, long and pointer are 64-bit)
• Unix and Unix-like systems (Linux, Mac OS X)

Other models are very rare. For example, ILP64 (8/8/8: int, long, and pointer are 64-bit) only appeared in some early 64-bit Unix systems (e.g. Unicos on Cray).

Note that exact-width integer types are available in <stdint.h> since C99.

Real floating types

C has three types for representing real floating-point values:

• float - single precision floating point type. Matches IEEE-754 32 bit floating point type if supported.
• double - double precision floating point type. Matches IEEE-754 64 bit floating point type if supported
• long double - extended precision floating point type. Matches IEEE-754 extended floating-point type if supported, otherwise matches some non-standard extended floating-point type as long as its precision is better than double and range is at least as good as double, otherwise matches the type double. Some x86 and x86_64 implementations use the 80-bit x87 floating point type.

Floating-point types may support special values:

• infinity (positive and negative), see INFINITY
• the negative zero, -0.0. It compares equal to the positive zero, but is meaningful in some arithmetic operations, e.g. 1.0/0.0 == INFINITY, but 1.0/-0.0 == -INFINITY)
• not-a-number (NaN), which does not compare equal with anything (including itself). Multiple bit patterns represent NaNs, see nan, NAN. Note that C takes no special notice of signalling NaNs (specified by IEEE-754), and treates all NaNs as quiet.

Real floating-point numbers may be used with arithmetic operators + - / * and various mathematical functions from math.h. Both built-in operators and library functions may raise floating-point exceptions and set errno as described in math_errhandling.

Floating-point expressions may have greater range and precision than indicated by their types, see FLT_EVAL_METHOD. Assignment, return, and cast force the range and precision to the one associated with the declared type.

Floating-point expressions may also be contracted, that is, calculated as if all intermediate values have infinite range and precision, see #pragma STDC FP_CONTRACT.

Some operations on floating-point numbers are affected by and modify the state of the floating-point environment (most notably, the rounding direction).

Implicit conversions are defined between real floating types and integer, complex, and imaginary types.

See Limits of floating point types and the math.h library for additional details, limits, and properties of the floating-point types.

#include <complex.h>
#include <stdio.h>
int main(void)
{
    double complex z = 1 + 2*I;
    z = 1/z;
    printf("1/(1.0+2.0i) = %.1f%+.1fi\n", creal(z), cimag(z));
}

1/(1.0+2.0i) = 0.2-0.4i

float a[4] = {1, 2, 3, 4};
float complex z1, z2;
memcpy(&z1, a, sizeof z1); // z1 becomes 1.0 + 2.0i
memcpy(&z2, a+2, sizeof z2); // z2 becomes 3.0 + 4.0i

#include <stdio.h>
#include <complex.h>
#include <math.h>
int main(void)
{
   double complex z = (1 + 0*I) * (INFINITY + I*INFINITY);
// textbook formula would give
// (1+i0)(∞+i∞) ⇒ (1×∞ – 0×∞) + i(0×∞+1×∞) ⇒ NaN + I*NaN
// but C gives a complex infinity
   printf("%f + i*%f\n", creal(z), cimag(z));
 
// textbook formula would give
// cexp(∞+iNaN) ⇒ exp(∞)×(cis(NaN)) ⇒ NaN + I*NaN
// but C gives  ±∞+i*nan
   double complex y = cexp(INFINITY + I*NAN);
   printf("%f + i*%f\n", creal(y), cimag(y));
 
}

inf + i*inf 
inf + i*nan

#include <complex.h>
#include <stdio.h>
int main(void)
{
    double imaginary z = 3*I;
    z = 1/z;
    printf("1/(3.0i) = %+.1fi\n", cimag(z));
}

1/(3.0i) = -0.3i

Keywords

char, int, short, long, signed, unsigned, float, double. _Bool, _Complex, _Imaginary.

Range of values

The following table provides a reference for the limits of common numeric representations. As the C Standard allows any signed integer representation, the table gives both the minimum guaranteed requirements (which correspond to the limits of one's complement or sign-and-magnitude) and the limits of the most commonly used implementation, two's complement. All popular data models (including all of ILP32, LP32, LP64, LLP64) use two's complement representation, though.

Note: actual (as opposed to guaranteed minimal) ranges are available in the library headers <limits.h> and <float.h>

See also