String literals placed side-by-side are concatenated at translation phase 6 (after the preprocessor). This feature is used to represent long string literal on multiple lines.

For instance, the following declarations are equivalent:

const char* A[] = "This is a test";
const char* B[] = "This" " is a "    "test";

A common mistake done by programmers is to forget a comma between two string literals in an array initializer list.

const char* Test[] = {
  "line 1",
  "line 2"     // Missing comma!
  "line 3",
  "line 4",
  "line 5"

The array contains the string “line 2line3” at offset 1 (i.e. Test[1]). Clang won’t generate warnings at compile time.

This check may warn incorrectly on cases like:

const char* SupportedFormat[] = {
  "Error %s",
  "Code " PRIu64,   // May warn here.
  "Warning %s",



An unsigned integer specifying the minimum size of a string literal to be considered by the check. Default is 5U.


A string specifying the maximum threshold ratio [0, 1.0] of suspicious string literals to be considered. Default is ”.2”.


An unsigned integer specifying the maximum number of concatenated tokens. Default is 5U.