Imaginary_I
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                    |   Defined in header  
<complex.h>
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|   #define Imaginary_I /* unspecified */ 
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(since C99) | |
The Imaginary_I macro expands to a value of type const float _Imaginary with the value of the imaginary unit. The macro is defined only if the implementation supports imaginary types. 
| This section is incomplete Reason: on what condition? The standard seems unclear. Maybe when __STDC_IEC_559_COMPLEX__ is defined?  | 
[edit] See also
|    (C99) 
 | 
   the complex unit constant i  (macro constant)  | 
|    (C99) 
 | 
   the complex or imaginary unit constant i  (macro constant)  |