计算经经php打包以后的包体的长度

 

$body_bin = pack('LLCCa16LL', $user_id, $free_cost,  $is_vip, $buy_placei, md5($passwd, true), $mb_product_count, $tongbao_produc
t_count);                                                                                                                          

$pkg_len = strlen($body_bin);
echo "package length : $pkg_len\n";

结果是：34

解析：

• a - NUL-padded string
• A - SPACE-padded string
• h - Hex string, low nibble first
• H - Hex string, high nibble first
• c - signed char
• C - unsigned char
• s - signed short (always 16 bit, machine byte order)
• S - unsigned short (always 16 bit, machine byte order)
• n - unsigned short (always 16 bit, big endian byte order)
• v - unsigned short (always 16 bit, little endian byte order)
• i - signed integer (machine dependent size and byte order)
• I - unsigned integer (machine dependent size and byte order)
• l - signed long (always 32 bit, machine byte order)
• L - unsigned long (always 32 bit, machine byte order)
• N - unsigned long (always 32 bit, big endian byte order)
• V - unsigned long (always 32 bit, little endian byte order)
• f - float (machine dependent size and representation)
• d - double (machine dependent size and representation)
• x - NUL byte
• X - Back up one byte
• @ - NUL-fill to absolute position

可以看出L代表unsigned long ，类型，占有4字节。C代表unsigned char类型，占有1字节。而“a+数字”就是 padded string 类型，长度为“数字”个字节的长度，所以a16

有长度为16个字节。

然后：4+4+1+1+16+4+4=34