String concatenation with a space

Question

In K&R, I saw an example where a string can be concatenated with a space"

char *s = "abc" "foo";
printf("%s", s); // prints "abcfoo"

How is space string concatenation different from using strcpy and strcat?

Answer 1

Adjacent string literal are concatenated by the pre-processor. From the draft C99 standard section 5.1.1.2 Translation phases paragraph 6:

Adjacent string literal tokens are concatenated

so it creates one string literal as a result.

Answer 2

Try: char *s = "abc" " " "foo";

BTW: it is not concatenation per se, it is just a method for initialising a string with a concatenation of a bunch of literals.