_Complex_I

#define _Complex_I /* unspecified */

The _Complex_I macro expands to a value of type const float _Complex with the value of the imaginary unit.

Notes

This macro may be used when I is not available, such as when it has been undefined by the application.

Unlike _Imaginary_I and CMPLX, use of this macro to construct a complex number may lose the sign of zero on the imaginary part.

Example

#include <stdio.h>
#include <complex.h>
 
#undef I
#define J _Complex_I // can be used to redefine I
 
int main(void)
{
    // can be used to construct a complex number
    double complex z = 1.0 + 2.0 * _Complex_I;
    printf("1.0 + 2.0 * _Complex_I = %.1f%+.1fi\n", creal(z), cimag(z));
 
    // sign of zero may not be preserved
    double complex z2 = 0.0 + -0.0 * _Complex_I;
    printf("0.0 + -0.0 * _Complex_I = %.1f%+.1fi\n", creal(z2), cimag(z2));
}

1.0 + 2.0 * _Complex_I = 1.0+2.0i
0.0 + -0.0 * _Complex_I = 0.0+0.0i

References

• C23 standard (ISO/IEC 9899:2023):
• 7.3.1/4 _Complex_I (p: TBD)
• C17 standard (ISO/IEC 9899:2018):
• 7.3.1/4 _Complex_I (p: 136)
• C11 standard (ISO/IEC 9899:2011):
• 7.3.1/4 _Complex_I (p: 188)
• C99 standard (ISO/IEC 9899:1999):
• 7.3.1/2 _Complex_I (p: 170)

See also