long x = '\xde\xad\xbe\xef'; // yes, single quotes
Surprisingly (to me at least), this is valid ISO 9899:1999 C. It compiles without warning under gcc with -Wall, and a “multi-character character constant” warning with -pedantic.
According to the standard (ยง6.4.4.4.10),
The value of an integer character constant containing more than one character (e.g.,
'ab'), […] is implementation-defined.
A bit of experimentation shows that gcc stores the leftmost character in the literal as the most-significant byte in the integer. But is this a reliable behavior in other common compilers? It’s a cool little piece of esoteric C syntax, but I’m guessing nobody interested in portable code should be using it when an integer constant works just as well.