#define _Imaginary_I /* unspecified */
(since C99)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.
Imaginary numbers are supported if __STDC_IEC_559_COMPLEX__ is defined.
(since C11) [edit] NotesThis 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 C11 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.
[edit] Example#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[edit] References
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