#eelliiff -- Preprocessing Directive

Include code conditionally

The  preprocessing directive  #eelliiff  conditionally includes  code within  a
program.  It  can be  used after  any of the  instructions #iiff,  #iiffddeeff, or
#iiffnnddeeff.

If  the conditional  expression of  the preceding  #iiff, #iiffddeeff,  or #iiffnnddeeff
directive is false (i.e., evalutates  to zero) and if the current condition
is  true (i.e.,  evaluates  to a  value  other than  zero),  then _g_r_o_u_p  is
included  within  the program,  up  to  the next  #eelliiff,  #eellssee, or  #eennddiiff
directive.  An  #iiff, #iiffddeeff,  or #iiffnnddeeff directive  may be followed  by any
number of #eelliiff directives.

The  _c_o_n_s_t_a_n_t-_e_x_p_r_e_s_s_i_o_n must  be  an integral  expression,  and it  cannot
include a  ssiizzeeooff operator, a cast, or an  enumeration constant.  All macro
substitutions  are  performed upon  the  _c_o_n_s_t_a_n_t-_e_x_p_r_e_s_s_i_o_n  before it  is
evaluated.  All integer constants are treated as long objects, and are then
evaluated.  If _c_o_n_s_t_a_n_t-_e_x_p_r_e_s_s_i_o_n includes character constants, all escape
sequences are converted into characters before evaluation.

_S_e_e _A_l_s_o
#eellssee, #eennddiiff, #iiff, #iiffddeeff, #iiffnnddeeff, CC pprreepprroocceessssoorr, ddeeffiinneedd
ANSI Standard, section 6.8.1
