_Imaginary_I

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.

[edit] 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 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));
}

z1 = 0.0+Infi 
z2 = NaN+Infi

[edit] References

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