imaginary

 

C

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Technical Specifications

 

Numerics

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Complex number arithmetic

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

 

Defined in header <complex.h>
#define imaginary _Imaginary		(since C99)

This macro expands to the keyword _Imaginary.

This is a convenience macro that makes it possible to use float imaginary, double imaginary, and long double imaginary as an alternative way to write the three pure imaginary C types float _Imaginary, double _Imaginary, and long double _Imaginary

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 C99) (until C11)
Imaginary numbers are supported if __STDC_IEC_559_COMPLEX__ is defined.	(since C11)

Notes

Programs are allowed to undefine and perhaps redefine the imaginary macro.

Example

Run this code

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

Output:

z = 1.0+2.0i

References

• C11 standard (ISO/IEC 9899:2011):

• 7.3.1/5 imaginary (p: 188)

• G.6/1 imaginary (p: 537)

• C99 standard (ISO/IEC 9899:1999):

• 7.3.1/3 imaginary (p: 170)

• G.6/1 imaginary (p: 472)

See also

complex (C99)

complex type macro (keyword macro)