c - How does concatenation of two string literals work?

Question

char* a="dsa" "qwe";
printf("%s", a);

output: dsaqwe

My question is why does this thing work. If I give a space or nothing in between two string literals it concatenates the string literals.

How is this working?

Answer 1

It's defined by the ISO C standard, adjacent string literals are combined into a single one.

The language is a little dry (it is a standard after all) but section 6.4.5 String literals of C11 states:

In translation phase 6, the multibyte character sequences specified by any sequence of adjacent character and identically-prefixed wide string literal tokens are concatenated into a single multibyte character sequence.

This is also mentioned in 5.1.1.2 Translation phases, point 6 of the same standard, though a little more succinctly:

Adjacent string literal tokens are concatenated.

This basically means that "abc" "def" is no different to "abcdef".

It's often useful for making long strings while still having nice formatting, something like:

const char *myString = "This is a really long "
                       "string and I don't want "
                       "to make my lines in the "
                       "editor too long, because "
                       "I'm basically anal retentive :-)";