According to MISRA 2008, concatenation of wide and narrow string literals leads to undefined behavior. This is an implicit undefined behavior according to the C standard was once considered implicitly undefined behavior. However, [ISO/IEC 9899:2011] does define this behavior, and it is further explained in C11. According to Section 6.4.5, paragraph 5:
In translation phase 6, the multibyte character sequences specified by any sequence of adjacent character and identically-prefixed string literal tokens are concatenated into a single multibyte character sequence. If any of the tokens has an encoding prefix, the resulting multibyte character sequence is treated as having the same prefix; otherwise, it is treated as a character string literal. Whether differently-prefixed wide string literal tokens can be concatenated and, if so, the treatment of the resulting multibyte character sequence are implementation-defined.
Nonetheless, it is recommended that string literals that are concatenated should all be the same type, so as not to rely on implementation-defined behavior, or undefined behavior if compiled on a platform that only supports C90.
Noncompliant Code Example
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