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# I

From cppreference.com
< c‎ | numeric‎ | complex

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] See also

Complex_I (C99) | the complex unit constant i (macro constant) [edit]
Imaginary_I (C99) | the imaginary unit constant i (macro constant) [edit]

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