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

[edit]Character types

• signedchar — type for signed character representation.
• unsignedchar — type for unsigned character representation. Also used to inspectobject representations (raw memory).
• char — type for character representation. Equivalent to eithersignedchar orunsignedchar (which one is implementation-defined and may be controlled by a compiler commandline switch), butchar is a distinct type, different from bothsignedchar andunsignedchar.

Note that the standard library also definestypedef nameswchar_t,char16_t andchar32_t(since C11) to represent wide charactersandchar8_t for UTF-8 characters(since C23).

[edit]Integer types

• shortint (also accessible asshort, may use the keywordsigned)
• unsignedshortint (also accessible asunsignedshort)
• int (also accessible assignedint)

This is the most optimal integer type for the platform, and is guaranteed to be at least 16 bits. Most current systems use 32 bits (see Data models below).

• unsignedint (also accessible asunsigned), the unsigned counterpart ofint, implementing modulo arithmetic. Suitable for bit manipulations.
• longint (also accessible aslong)
• unsignedlongint (also accessible asunsignedlong)

Note: as with all type specifiers, any order is permitted:unsignedlonglongint andlongintunsignedlong 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(longlong).

Note: this allows the extreme case in whichbyte are sized 64 bits, all types (includingchar) are 64 bits wide, andsizeof returns1 for every type.

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

[edit]Data models

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

32 bit systems:

• LP32 or2/4/4 (int is 16-bit,long and pointer are 32-bit)

• Win16 API

• ILP32 or4/4/4 (int,long, and pointer are 32-bit);

• Win32 API
• Unix and Unix-like systems (Linux, Mac OS X)

64 bit systems:

• LLP64 or4/4/8 (int andlong are 32-bit, pointer is 64-bit)

• Win64 API

• LP64 or4/8/8 (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.

[edit]Real floating types

C has threeor six(since C23) types for representing real floating-point values:

• float — single precision floating-point type. MatchesIEEE-754 binary32 format if supported.
• double — double precision floating-point type. MatchesIEEE-754binary64 format if supported.
• longdouble — extended precision floating-point type. MatchesIEEE-754binary128 format if supported, otherwise matchesIEEE-754binary64-extended format if supported, otherwise matches some non-IEEE-754 extended floating-point format as long as its precision is better thanbinary64 and range is at least as good asbinary64, otherwise matches IEEE-754binary64 format.
  • binary128 format is used by some HP-UX, SPARC, MIPS, ARM64, and z/OS implementations.
  • The most well known IEEE-754binary64-extended format is 80-bit x87 extended precision format. It is used by many x86 and x86-64 implementations (a notable exception is MSVC, which implementslongdouble in the same format asdouble, i.e.binary64).

Floating-point types may support special values:

• infinity (positive and negative), seeINFINITY
• thenegative zero,-0.0. It compares equal to the positive zero, but is meaningful in some arithmetic operations, e.g.1.0/0.0== INFINITY, but1.0/-0.0==-INFINITY)
• not-a-number (NaN), which does not compare equal with anything (including itself). Multiple bit patterns represent NaNs, seenan,NAN. Note that C takes no special notice of signaling NaNs (specified by IEEE-754), and treats all NaNs as quiet.

Real floating-point numbers may be used witharithmetic operators+-/* and various mathematical functions from<math.h>. Both built-in operators and library functions may raise floating-point exceptions and seterrno as described inmath_errhandling.

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

Floating-point expressions may also becontracted, 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 ofthe floating-point environment (most notably, the rounding direction).

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

SeeLimits 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){doublecomplex 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};floatcomplex z1, z2;memcpy(&z1, a,sizeof z1);// z1 becomes 1.0 + 2.0imemcpy(&z2, a+2,sizeof z2);// z2 becomes 3.0 + 4.0i

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

inf+inf*i inf+nan*i

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

1/(3.0i) = -0.3i

[edit]Keywords

• bool,true,false,char,int,short,long,signed,unsigned,float,double.
• _Bool,_BitInt,_Complex,_Imaginary,_Decimal32,_Decimal64,_Decimal128.

[edit]Range of values

The following table provides a reference for the limits of common numeric representations.

Prior to C23, the C Standard allowed any signed integer representation, and the minimum guaranteed range of N-bit signed integers was from\(\scriptsize -(2^{N-1}-1)\)-(2N-1
-1) to\(\scriptsize +2^{N-1}-1\)+2N-1
-1 (e.g.-127 to127 for a signed 8-bit type), which corresponds to the limits ofone's complement orsign-and-magnitude.

However, all popular data models (including all of ILP32, LP32, LP64, LLP64) and almost all C compilers usetwo's complement representation (the only known exceptions are some compilers for UNISYS), and as of C23, it is the only representation allowed by the standard, with the guaranteed range from\(\scriptsize -2^{N-1}\)-2N-1
to\(\scriptsize +2^{N-1}-1\)+2N-1
-1 (e.g.-128 to127 for a signed 8-bit type).

1. ↑The object representation usually occupies 96/128 bits on 32/64-bit platforms respectively.

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

[edit]See also

• In other languages

• العربية
• Česky
• Deutsch
• Español
• Français
• Italiano
• 日本語
• 한국어
• Polski
• Português
• Русский
• Türkçe
• 中文