_Imaginary_I

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Complex number arithmetic
Types and the imaginary constant
 imaginary _Imaginary_I I
Manipulation
Power and exponential functions
Trigonometric functions
Hyperbolic functions

 Defined in header `` #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. (since C99)(until C11) Imaginary numbers are supported if __STDC_IEC_559_COMPLEX__ is defined. (since C11)

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.

Example

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

int main(void)
{
double complex z = 0.0 + -0.0 * _Imaginary_I;
printf("z = %.1f%+.1fi\n", creal(z), cimag(z));
}```

Output:

`z = 0.0-0.0i`

References

• C11 standard (ISO/IEC 9899:2011):
• 7.3.1/5 _Imaginary_I (p: 188)
• G.6/1 _Imaginary_I (p: 537)
• C99 standard (ISO/IEC 9899:1999):
• 7.3.1/3 _Imaginary_I (p: 170)
• G.6/1 _Imaginary_I (p: 472)