php pack与unpack 摸板字符字符含义
format 参数的可能值: a - NUL-padded string A - SPACE-padded string h - Hex string, low nibble first H - Hex string, high nibble first c - signed char C - un
format 参数的可能值: a - NUL-padded string A - SPACE-padded string h - Hex string, low nibble first H - Hex string, high nibble first c - signed char C - un