_Complex_I

C

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Headers

Type support

Program utilities

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Error handling

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Date and time utilities

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Input/output support

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Atomic operations (C11)

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Technical Specifications

Numerics

Common mathematical functions

Floating-point environment

Complex number arithmetics

Random number generation

Type-generic math

Complex number arithmetic

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

Defined in header <complex.h>
#define _Complex_I /* unspecified */		(since C99)

The _Complex_I macro expands to a value of type const float _Complex with the value of the imaginary unit.

Notes

This macro may be used when I is not available, such as when it has been undefined by the application.

Unlike _Imaginary_I and CMPLX, use of this macro to construct a complex number may lose the sign of zero on the imaginary component.

Example

Run this code

#include <stdio.h>
#include <complex.h>

#undef I
#define J _Complex_I // can be used to redefine I

int main(void)
{
    // can be used to construct a complex number
    double complex z = 1.0 + 2.0 * _Complex_I;
    printf("1.0 + 2.0 * _Complex_I =%.1f%+.1fi\n", creal(z), cimag(z));

    // sign of zero may not be preserved
    double complex z2 = 0.0 + -0.0 * _Complex_I;
    printf("0.0 + -0.0 * _Complex_I =%.1f%+.1fi\n", creal(z2), cimag(z2));
}

Possible output:

1.0 + 2.0 * _Complex_I = 1.0+2.0i
0.0 + -0.0 * _Complex_I = 0.0+0.0i

References

• C11 standard (ISO/IEC 9899:2011):

• 7.3.1/4 _Complex_I (p: 188)

• C99 standard (ISO/IEC 9899:1999):

• 7.3.1/2 _Complex_I (p: 170)

See also

_Imaginary_I (C99)	the imaginary unit constant i (macro constant)
I (C99)	the complex or imaginary unit constant i (macro constant)