Defined in header `<complex.h>` | ||
---|---|---|

#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 |
(since C99) (until C11) |

Imaginary numbers are supported if | (since C11) |

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.

#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

- 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)

(C99) | the complex unit constant i (macro constant) |

(C99) | the complex or imaginary unit constant i (macro constant) |

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