lex_pptoken.md

• A preprocessing token is the minimal lexical element of the language in translation phases 3 through 6. … If a ’ or a " character matches the last category, the behavior is undefined. [lex.pptoken]/p2
  • Example Why can't we use the preprocessor to create custom-delimeted strings?

#define STR_START "
#define STR_END "

int puts(const char *);

int main() {
    puts(STR_START hello world STR_END);
}

• Discussion
  • Should it be ill-formed
• Rationale
  • Preprocessing token are generated during phase 3 so string and character literals as well and header names are identified at this point. both ‘ and “ would only be valid as part of one of these tokens, any left over after this point perhaps as part of a macro would not be valid since they could not tokenized as needed anymore. Macros are expanded as part of phase 4.