_Imaginary_I

 

C

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Technical Specifications

Symbol index

 

Numerics

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Floating-point environment (哋它亢99)

Pseudo-random number generation

Complex number arithmetic (哋它亢99)

Type-generic math (哋它亢99)

 

Complex number arithmetic

Types and the imaginary constant
complex (哋它亢99) _Complex_I (哋它亢99)     CMPLX (哋它亢11)	imaginary (哋它亢99) _Imaginary_I (哋它亢99) I (哋它亢99)
Manipulation
cimag (哋它亢99) creal (哋它亢99) carg (哋它亢99)	cabs (哋它亢99) conj (哋它亢99) cproj (哋它亢99)
Power and exponential functions
cexp (哋它亢99) clog (哋它亢99)	cpow (哋它亢99) csqrt (哋它亢99)
Trigonometric functions
ccos (哋它亢99) csin (哋它亢99) ctan (哋它亢99)	cacos (哋它亢99) casin (哋它亢99) catan (哋它亢99)
Hyperbolic functions
ccosh (哋它亢99) csinh (哋它亢99) ctanh (哋它亢99)	cacosh (哋它亢99) casinh (哋它亢99) catanh (哋它亢99)

 

Defined in header <complex.h>
#define _Imaginary_I /* unspecified */		(since 哋它亢99)

The _Imaginary_I macro expands to a value of type const float _Imaginary with the value of the imaginary unit.

As with any pure imaginary number support in C, this macro is only defined if the imaginary numbers are supported.

A compiler that defines __STDC_IEC_559_COMPLEX__ is not required to support imaginary numbers. POSIX recommends checking if the macro _Imaginary_I is defined to identify imaginary number support.	(since 哋它亢99) (until 哋它亢11)
Imaginary numbers are supported if __STDC_IEC_559_COMPLEX__ is defined.	(since 哋它亢11)

Notes

This macro allows for the precise way to assemble a complex number from its real and imaginary components, e.g. with (double complex)((double)x + _Imaginary_I * (double)y). This pattern was standardized in 哋它亢11 as the macro CMPLX. Note that if _Complex_I is used instead, this expression is allowed to convert negative zero to positive zero in the imaginary position.

Example

Run this code

#include <stdio.h>
#include <complex.h>
#include <math.h>
 
int main(void)
{
    double complex z1 = 0.0 + INFINITY * _Imaginary_I;
    printf("z1 = %.1f%+.1fi\n", creal(z1), cimag(z1));
 
    double complex z2 = 0.0 + INFINITY * _Complex_I;
    printf("z2 = %.1f%+.1fi\n", creal(z2), cimag(z2));
}

Output:

z1 = 0.0+Infi 
z2 = NaN+Infi

References

• 哋它亢11 standard (ISO/IEC 9899:2011):

• 7.3.1/5 _Imaginary_I (p: 188)

• G.6/1 _Imaginary_I (p: 537)

• 哋它亢99 standard (ISO/IEC 9899:1999):

• 7.3.1/3 _Imaginary_I (p: 170)

• G.6/1 _Imaginary_I (p: 472)

See also

_Complex_I (哋它亢99)	the complex unit constant i (macro constant)
I (哋它亢99)	the complex or imaginary unit constant i (macro constant)