#uunnddeeff -- Preprocessing Directive

Undefine a macro
#uunnddeeff _i_d_e_n_t_i_f_i_e_r

The preprocessing  directive #uunnddeeff tells  the C preprocessor  to disregard
_i_d_e_n_t_i_f_i_e_r as a macro.  It undoes the effect of the #ddeeffiinnee directive.

_S_e_e _A_l_s_o
#ddeeffiinnee, CC pprreepprroocceessssoorr
ANSI Standard, section 6.8.3
