diff --git a/src/string_func.h b/src/string_func.h
--- a/src/string_func.h
+++ b/src/string_func.h
@@ -40,6 +40,7 @@ int CDECL vseprintf(char *str, const cha
 char *CDECL str_fmt(const char *str, ...) WARN_FORMAT(1, 2);
 
 void str_validate(char *str, const char *last, StringValidationSettings settings = SVS_REPLACE_WITH_QUESTION_MARK);
+std::string str_validate(const std::string &str, StringValidationSettings settings = SVS_REPLACE_WITH_QUESTION_MARK);
 void ValidateString(const char *str);
 
 void str_fix_scc_encoded(char *str, const char *last);