使用PHP int的开销是多少？ [英] What is the overhead of using PHP int?

问题描述

我一直听说PHP有开销。例如，C ++ int在32位系统上使用4字节，但PHP int使用更多。这个值是多少？

I keep hearing that PHP has overhead. For example a C++ int uses 4 Bytes on a 32 bit system but a PHP int uses more. What is this value?

推荐答案

我需要更多空间而不是评论来扩展马里奥的发现，所以我会添加一个答案而不是。

I need more space than a comment to expand on mario's findings so I'll add an answer instead.

C union 的大小将是其最大成员的大小（可能需要额外的字节数）对齐约束）。对于 zvalue_value ，这将是 obj ，其大小为三个指针（不包括这些指针所需的内存）指针指向）：

The size of a C union will be the size of its largest member (possibly with extra bytes to satisfy alignment constraints). For zvalue_value, that would be the obj which has the size of three pointers (not including the memory required for what those pointers point to):

typedef struct _zend_object {
    zend_class_entry *ce;
    HashTable *properties;
    HashTable *guards; /* protects from __get/__set ... recursion */
} zend_object;

在32位系统上， zend_object 将在64位系统上占用24个字节，需要48个字节。因此，无论您在其中存储什么数据，每个 zvalue_value 将至少需要24或48个字节。还有变量的名称，它消耗更多的内存;编译语言通常在编译器完成后丢弃名称，并将值视为简单的字节序列（因此 double 需要8个字节， char 需要一个字节等...）。

On a 32bit system, a zend_object will take 24 bytes while on a 64bit system it will take 48 bytes. So, every zvalue_value will take at least 24 or 48 bytes regardless of what data you store in it. There's also the name of the variable which consumes more memory; compiled languages generally discard the names once the compiler is done and treat values as simple sequences of bytes (so a double takes eight bytes, a char takes one byte, etc...).

关于你最近关于PHP布尔值的问题，一个简单的布尔值将消耗24或48个字节对于值，再加上几个字节的名称，再加上四个或八个 zend_unit ，再加上四个（或八个）的两个 zend_uchar s在此：

With regards to your recent questions about PHP booleans, a simple boolean value will consume 24 or 48 bytes for the value, plus a few more bytes for the name, plus four or eight for the zend_unit, plus four (or eight) for the two zend_uchars in this:

struct _zval_struct {
    /* Variable information */
    zvalue_value value;     /* value */
    zend_uint refcount__gc;
    zend_uchar type;    /* active type */
    zend_uchar is_ref__gc;
};

zend_uchar 会员将嚼四（或者八个字节由于对齐约束，几乎每个CPU都希望访问自然地址边界上的内存，这意味着 struct 的单个字节大小的成员将占用四个字节或八个字节的内存（取决于CPU的自然字大小和对齐约束）。因此，布尔值将占用36到72个字节的内存。

The zend_uchar members will chew up four (or eight) bytes due to alignment constraints, almost every CPU wants to access memory on natural address boundaries and that means that a single byte sized member of a struct will take up four bytes or eight bytes of memory (depending on the CPUs natural word size and alignment constraints). So, a boolean will take somewhere between 36 and 72 bytes of memory.

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