(PHP 6 >= 6.0.0)
unicode_set_subst_char — Set the substitution character for string conversion errors
When converting a string from or to unicode, an invalid or unconvertible character may be encountered. When the conversion error mode is set to U_CONV_ERROR_SUBST, the character that caused the error is substituted by a character set by this function. The default substitution character is ?.
The substitution character to use.
如果成功则返回 TRUE，失败则返回 FALSE。
Emits a E_WARNING level error if character is invalid.
本函数是实验性的。本函数的行为，包括函数名称以及其它任何关于本函数的文档可能会在没有通知的情况下随 PHP 以后的发布而改变。使用本函数风险自担。