String contants special characters

Ex:
s = "abc??(x)";

Compile error by '-trigraphs' option of compiler,
??=、??(、??/、??)、??'、??<、??!、??>、??-  is each #、[、¥、]、^、{、|、}、̃
"abc??(x)" is "abc[x)".

Fix:
s = "abc\?\?(x)";