hash_update()

(PHP 5 >= 5.1.2, PHP 7, PECL hash >= 1.1)

向活跃的哈希运算上下文中填充数据

说明

hash_update(HashContext$context,string $data): bool

参数

$context

由hash_init()函数返回的哈希运算上下文。

$data

要向哈希摘要中追加的数据。

返回值

返回TRUE。

更新日志

参见

• hash_init() 初始化增量哈希运算上下文
• hash_update_file() 从文件向活跃的哈希运算上下文中填充数据
• hash_update_stream() 从打开的流向活跃的哈希运算上下文中填充数据
• hash_final() 结束增量哈希，并且返回摘要结果

A simple example on incremental file hashing:
$fp = fopen($file, "r");
$ctx = hash_init('sha256');
while (!feof($fp)) {
  $buffer = fgets($fp, 65536);
  hash_update($ctx, $buffer);
}
$hash = hash_final($ctx, true);
fclose($fp);
While incremental hashing is quite slow, it's the easiest way to hash 
- parts of large files: I.e., a 700MB avi video uses first x bytes to store metadata, so in order to hash the avi's data only, you have to fseek to data start and use incremental hashing
- streaming data if php just proxies the data
- whenever it's inadequate or impossible to store the data being hashed into memory (i.e. because of their size) or on disc.