Why allow concatenation of string literals?

I was recently bitten by a subtle bug.

char ** int2str = {
   "zero", // 0
   "one",  // 1
   "two"   // 2
   "three",// 3
   nullptr };

assert( int2str[1] == std::string("one") ); // passes
assert( int2str[2] == std::string("two") ); // fails

If you have godlike code review powers, you'll notice I forgot the , after "two".

After the considerable effort to find that bug, I've got to ask why would anyone ever want this behavior?

I can see how this might be useful for macro magic, but then why is this a "feature" in a modern language like Python?

Have you ever used string literal concatenation in production code?


  • I see several C and C++ answers but none of the really answer why or really what was the rationale for this feature? In C++ this is feature comes from C99 and we can find the rationale for this feature by going to Rationale for International Standard—Programming Languages—C section 6.4.5 String literals which says (emphasis mine):

    A string can be continued across multiple lines by using the backslash–newline line continuation, but this requires that the continuation of the string start in the first position of the next line. To permit more flexible layout, and to solve some preprocessing problems (see §6.10.3), the C89 Committee introduced string literal concatenation. Two string literals in a row are pasted together, with no null character in the middle, to make one combined string literal. This addition to the C language allows a programmer to extend a string literal beyond the end of a physical line without having to use the backslash–newline mechanism and thereby destroying the indentation scheme of the program. An explicit concatenation operator was not introduced because the concatenation is a lexical construct rather than a run-time operation.

    Python which seems to have the same reason, this reduces the need for ugly \ to continue long string literals. Which is covered in section 2.4.2 String literal concatenation of the The Python Language Reference.