+extern bool c_isalnum (int c) _GL_ATTRIBUTE_CONST;
+extern bool c_isalpha (int c) _GL_ATTRIBUTE_CONST;
+extern bool c_isblank (int c) _GL_ATTRIBUTE_CONST;
+extern bool c_iscntrl (int c) _GL_ATTRIBUTE_CONST;
+extern bool c_isdigit (int c) _GL_ATTRIBUTE_CONST;
+extern bool c_islower (int c) _GL_ATTRIBUTE_CONST;
+extern bool c_isgraph (int c) _GL_ATTRIBUTE_CONST;
+extern bool c_isprint (int c) _GL_ATTRIBUTE_CONST;
+extern bool c_ispunct (int c) _GL_ATTRIBUTE_CONST;
+extern bool c_isspace (int c) _GL_ATTRIBUTE_CONST;
+extern bool c_isupper (int c) _GL_ATTRIBUTE_CONST;
+extern bool c_isxdigit (int c) _GL_ATTRIBUTE_CONST;