Detailed explanation of array pointers in php

This article mainly shares with you the detailed explanation of the array pointer in PHP. First, we will share with you the operation method of the PHP array pointer. We hope it can help you.

1. PHP array pointer operation

Use PHP’s built-in functions: key, current, next(), prev() to move to the previous one,

reset() resets, moves to the first element, end() moves to the last element

Note that once the pointer position is illegal, relative movement (next, prev) cannot be done, Can move absolutely (reset, end), reset, used more frequently!

each() combines the functions of key, current, and next! After obtaining the current element information, move the pointer to the next element!

Element information array = each($arr).Move pointer

Note that element information array has two representation schemes: index and association.

Including: Index: 0, 1 represents key and value respectively, association: key, value represents key and value respectively

2. Commonly used pointer traversal methods

each+while+list Traverse the array

list-eachTraverse the array

Upgrade Operation:

The operation that will obtain key variables and value variables, simplified!

Use the list structure

Use an index array to initialize multiple variables at the same time! The return value of

##each

contains the index array 0 as the key, 1 is the value!

Simplified results using list:

##In fact: as long as there is a loop structure, pointer operations can complete traversing the array

3. Discussion of array pointer issues

When considering copying Pointer position problem:

What if the original array pointer is already illegal?

Look again:

The question is, after copying, who executes current first and which array pointer is initialized!

The reasons for this phenomenon are:

1. If the array pointer position is illegal, the new array pointer will be initialized during copying!

2. When passing by value, PHP adopts a COW (copy on write) optimization measure!

Two key points of copy-on-write:

When the value is transferred, the value space is not immediately opened for the new variable, and before both variables have changed, one is still used. Value space

Once a variable changes, the value space will be copied, allowing the changed variable to reference the new space!

#Note that current will also issue write operations, causing the space to be copied! Whoever is current first is the new one, and the pointer is initialized!

foreach

1, what is traversed is copy Instead of the original array!

2, Only when a write operation occurs in the original array, the actual copy will be made. At this time, the original array pointer stays at the current position. If it is illegal, it will be initialized!

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