c++ - Is it valid to use boolean literals in preprocessor conditionals? -


consider following code, results in boolean literal true being evaluated in preprocessor conditional:

#define some_macro true  int main () { #if some_macro   return 1; #else   return 0; #endif }

clang 3.4 , gcc 4.8 both accept code, -pedantic -std=c++11 -wall -wextra.

visual studio 2013 rejects it, fatal error c1017: invalid integer constant expression.

my reading of n3376 § 16.1 regular c++ rules evaluating constant expressions should apply.

if so, code valid, , it's bug if msvc not accept it.

but don't find standardeze particularly clear. confirm this?

yes, valid. see c++11 §16.1/4 (emphasis mine)

prior evaluation, macro invocations in list of preprocessing tokens become controlling constant expression replaced (except macro names modified defined unary operator), in normal text. if token defined generated result of replacement process or use of defined unary operator not match 1 of 2 specified forms prior macro replacement, behavior undefined. after replacements due macro expansion , defined unary operator have been performed, all remaining identifiers , keywords, except true , false, replaced pp-number 0, , each preprocessing token converted token. resulting tokens comprise controlling constant expression evaluated according rules of 5.19 using arithmetic has @ least ranges specified in 18.3. purposes of token conversion , evaluation signed , unsigned integer types act if have same representation as, respectively, intmax_t or uintmax_t (18.4). includes interpreting character literals, may involve converting escape sequences execution character set members. whether numeric value these character literals matches value obtained when identical character literal occurs in expression (other within #if or #elif directive) implementation-defined. also, whether single-character character literal may have negative value implementation-defined. each subexpression type bool subjected integral promotion before processing continues.


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