hash_update

(PHP 5 >= 5.1.2, PHP 7, PHP 8, PECL hash >= 1.1)

hash_update — 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

版本	说明
7.2.0	接收参数从资源类型修改为 HashContext 对象类型。

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

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User Contributed Notes 1 note

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Dainichi ¶

15 years ago


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.

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