I
From cppreference.com
| Defined in header
<complex.h>
|
||
| #define I /* unspecified */
|
(since C99) | |
The I macro expands to either Complex_I or Imaginary_I. If the implementation does not support imaginary types, then the macro always expands to Complex_I.
| This section is incomplete Reason: on what condition imaginary types are supported? The standard seems unclear. Maybe when __STDC_IEC_559_COMPLEX__ is defined? |
A program may undefine and perhaps then redefine the imaginary macro.
[edit] Example
Run this code
#include <stdio.h> #include <complex.h> int main(void) { #ifdef __STDC_NO_COMPLEX__ printf("__STDC_NO_COMPLEX__ is defined.\n"); #else printf("__STDC_NO_COMPLEX__ is undefined.\n"); #endif #ifdef __STDC_IEC_559_COMPLEX__ printf("__STDC_IEC_559_COMPLEX__ is defined.\n"); #else printf("__STDC_IEC_559_COMPLEX__ is undefined.\n"); #endif printf("I = %.1f%+.1fi\n", creal(I), cimag(I)); printf("sizeof(I) = %zu\n", sizeof(I)); printf("sizeof(_Complex_I) = %zu\n", sizeof(_Complex_I)); double complex z = 1.0 + 2.0*I; printf("z = %.1f%+.1fi\n", creal(z), cimag(z)); return 0; }
Output:
__STDC_NO_COMPLEX__ is undefined. __STDC_IEC_559_COMPLEX__ is defined. I = 0.0+1.0i sizeof(I) = 8 sizeof(_Complex_I) = 8 z = 1.0+2.0i
[edit] See also
| (C99)
|
the imaginary unit constant i (macro constant) |
| (C99)
|
the complex unit constant i (macro constant) |
| (C11)(C11)(C11)
|
constructs a complex number from real and imaginary parts (function macro) |
|
C++ documentation for operator""i
|
|