Detailed explanation of commonly used system functions in php

This article mainly introduces the detailed explanation of commonly used system functions in PHP. Interested friends can refer to it. I hope it will be helpful to everyone.

String function

strlen: Get the string length, byte length

substr: String interception, get the string (according to bytes Intercept)

strchr: Similar to substr, intercept from the specified position until the end

strrchr (get the file suffix name): Same as strchr, just search for characters

# starting from the right ##strtolower: All characters are lowercase (for English letters)

strtoupper: All characters are uppercase

strrev: String reverse (only English can be reversed: there is only one English storage Bytes), reverse by bytes

strpos: Find the position (numeric subscript) where the corresponding character appears in the string, start from the leftmost

strrpos: Same as strpos , just start looking from the right side of the string

trim: remove the characters on both sides of the function, the default is spaces

Time and date function

time: get The timestamp of the current time (integer: starting from 0:00:00 GMT on January 1, 1970) in seconds

date: time serialization function, converts the specified timestamp into Specify the display format of time and date (arbitrary string: professional formatting regulations). If no timestamp is specified, the system defaults to the timestamp of the current time.

strtotime: Convert a string in time and date format to The corresponding timestamp (as long as it is a correct English time expression, it can be converted)

microtime: microsecond timestamp, returns different results according to different requirements. Mixed microtime (Boolean type), can return a Floating point time, can also return an array (timestamp and microseconds)

Mathematical related functions

abs: absolute value

floor : Round down floor(3.2) and the result is equal to 3

ceil: Round up

round: Round off

rand: Get a random integer within the specified range

mt_rand: Get a random integer within the specified range (more efficient)

Array related functions

key: Get the current pointer pointed to by the current array The subscript of the element

current: The obtained value of the current pointer pointing to the element

next: Get the value of the next element and move the pointer down

prev: Get the previous The value of an element, and moves the pointer up

end: moves the pointer to the last element of the array, and returns the value of the final pointer position

reset: moves the pointer to the first element of the array An element, returns the value of the final pointer position

array_keys: Gets all the key names of an array, returns an index array

array_values: Gets all the values of an array, returns an index array

explode: Explode, divide a string into multiple segments according to a specified rule (usually special characters), each segment is treated as an element of the array, and an index array is returned

implode: gluing, splicing all the elements inside an array into a string according to a specified rule (special characters)

array_merge: merging, referring to two The elements in the array are accumulated. If the subsequent array has the same subscript (key name: association) as the previous array, then the value of the subsequent element will overwrite the previous one; if it is the same subscript of the index, the subscript will be automatically modified and superimposed on the previous array. inside.

Data structure simulation function

array_shift: Pop elements from the front of the array and get the value of the element

array_pop: Pop elements from the back of the array, Get the value of the element

array_unshift: Push elements from the front of the array to get the number of current array elements

array_push: Push elements from the back of the array to get the number of current array elements

Determine the variable

is_bool: Determine whether it is a Boolean type

is_float: Determine the floating point type

is_integer: Determine the integer type

is_object: Judgment object

is_array: Judgment array

is_string: Judgment string

is_resource: Judgment resource

is_scalar: scalar It is scalar, and the basic data types are judged: integer, floating point, Boolean and string.

is_null: Whether it is empty.

is_numeric: Judgment of characters composed of numbers or pure numbers. String

gettype: Get the data type

settype: Change the data type

File operation function

opendir (path): open A path resource (read all data inside the path into memory)

readdir (path resource): Read the name of the file pointed to by the current resource pointer from the folder resource, and the pointer will move downward by one Bit

closedir (resource): Release the corresponding file resource

scandir (path): Read all file names inside a path and return an array. Each element of the array is a file name.

file_exists: Determine whether a file exists (file is a broad sense: path and file)

is_dir: Determine whether a specified path exists (folder)

is_file: Determine a Specify whether the path is a file (file)

mkdir: Create a path, if the path exists, an error will be reported

rmdir: Remove the folder

file_get_contents: Read data contents from a specified file.

file_put_contents: Write the specified string to the corresponding file

fopen: Open a file resource

fgetc: c represents character, read one character at a time

fgets: s represents string, which means multiple characters can be read, depending on the specified read length or whether a newline is encountered (only one line of data can be read at most)

Both functions are Operate on the current resource pointer, and the pointer will be moved down after reading.

fread: Get the data of the specified length until the end of the file.

fwrite: Write data to the location of the file resource pointer. Writing things will not move the existing things back at the current location, but will overwrite them.

fseek: Specify the pointer to the corresponding location

fclose: Use the corresponding file resource

copy: copy

unlink: delete file

rename: rename file

filemtime: m represents modify, the time when the file was last modified

filesize: File size (bytes)

fileperms: File permissions (octal under Linux)

The above is the entire content of this article, I hope it will be useful for everyone’s learning helped.

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