Implementation of string literal concatenation in C and C++

Question

AFAIK, this question applies equally to C and C++

Step 6 of the \"translation phases\" specified in the C standard (5.1.1.

Answer 1

There are tricky rules for how string literal concatenation interacts with escape sequences. Suppose you have

const char x1[] = "a\15" "4";
const char y1[] = "a\154";
const char x2[] = "a\r4";
const char y2[] = "al";

then x1 and x2 must wind up equal according to strcmp, and the same for y1 and y2. (This is what Heath is getting at in quoting the translation steps - escape conversion happens before string constant concatenation.) There's also a requirement that if any of the string constants in a concatenation group has an L or U prefix, you get a wide or Unicode string. Put it all together and it winds up being significantly more convenient to do this work as part of the "compiler" rather than the "preprocessor."