In the case of an unsigned long, the is_signed flag of the specialized variant numeric_limits 在无符号(unsigned)的long类型的情况下,专用变体numericlimits
Unsigned long remove_all ( const path & p ): This API attempts to remove a file or directory referred by path p.Unlike remove, it makes no special consideration for directories that are not empty. unsignedlongremoveall(constpath&p):此API尝试删除路径p所引用的文件或目录。与remove不同,此函数并不会特殊考虑不为空的目录。