c - How to make #if #endif part of a macro -

- 

#define m(n)\ #if n == 5\     /*several lines of code        can't replaced          tertnary operator*/ #else\     n;\ #endif

when use macro so

m(5);

i expect output 

// within #if #else block

but doesn't compile.

i'm not surprised doesn't compile: know #if cannot used on continuation line ie "\".

i've tried 

#define pound_if #if

and use pound_if doesn't work.

is possible do?

is there nifty boost pre-processor stuff can used?

succinctly, can't. can rely on optimizer instead, though:

#define m(n)\     { if (n == 5) { \     /*several lines of code        can't replaced          ternary operator*/ \     } else { n; } } while (0)

if compiler can determine value of n 5 when code run (e.g. write m(5)), code in body of if included in generated code. if compiler can determine value of n not 5 when code run, generate code in body of else clause. , if can't determine value be, preprocessor not have been able either, compiler include code.


Comments

Post a Comment

Popular posts from this blog

matlab - error with cyclic autocorrelation function -

-
Image
i'm trying code cyclic autocorrelation function in matlab follows: t=0:(n-1); t=t*te; i_alpha=0; tau=-n2*te:te:n2*te; alpha=-1/2:1/n:1/2; ryy_cl=zeros(length(alpha),length(tau)); alpha=alpha/te ind_tau=0; i_alpha=i_alpha+1; k=tau ind_tau=ind_tau+1; if k>0 % ryy_cl(i_alpha,ind_tau)=1/length(sig_bin_syl_mod(1:end- k))*sum((sig_bin_syl_mod(1:end-k)).*sig_bin_syl_mod(k+1:end)).*exp(1i*2*pi*alpha*t(1+k:length(sig_bin_syl_mod(1:end)))); ryy_cl(i_alpha,ind_tau)=(1/n)*sum((sig_bin_syl_mod(1:end-k)).*sig_bin_syl_mod(k+1:end)).*exp(-1i*2*pi*alpha*t(1:end-k)); else ryy_cl(i_alpha,ind_tau)=(1/n)*sum((sig_bin_syl_mod(1-k:end)).*sig_bin_syl_mod(1:end+k)).*exp(-1i*2*pi*alpha*t(1-k:end)); end end end i'm getting errors, , doesn't show expecting. according below formulae, how can fix it? the code provided incomplete, difficult confidently reproduce error. in particular, haven't de...
Read more

django - (fields.E300) Field defines a relation with model 'AbstractEmailUser' which is either not installed, or is abstract -

-
i trying create customuser django project email username , add radio button truck , company. in registration process email-id registered per truck or company. mentioned radio button 'tag' , add manytomany field tag in emailuser model. when makemigrations, raising error : (fields.e300) field defines relation model 'abstractemailuser' either not installed, or abstract. i quite new django , not sure whether have created correct code wants. please me solving this. here code, models.py: import django django.contrib.auth.models import ( abstractbaseuser, baseusermanager, permissionsmixin) django.core.mail import send_mail django.db import models django.utils import timezone django.utils.translation import ugettext_lazy _ class emailusermanager(baseusermanager): """custom manager emailuser.""" def _create_user(self, email, password, is_staff, is_superuser, **extra_fields): """create , save emailus...
Read more

c# - What is a good .Net RefEdit control to use with ExcelDna? -

-
i using exceldna , c# build suite of tools. part of forms i'd want user select cells/ranges workbook. i've got application.inputbox route working...but doesn't cool... i haven't read many things excel's refedit control, , see many have in past written workarounds, in (shudder) vba or vb.net. however, none of these seem recent... best approach/control refedit functionality on form run via exceldna (if applicable)? the refedit sample project of github explores different ways of dealing threading when showing form excel add-in, main issue making refedit control .net add-in. check page links various other implementations: https://github.com/excel-dna/exceldna/wiki/links-about-refedit
Read more