Summary of commonly used system functions in php

This article introduces the commonly used system functions in php, which has a good reference value. Let’s take a look at it with the editor

String function

strlen : Get the string length, byte length

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

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

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

strtolower: All characters are lowercase (for English letters)

strtoupper: All characters are uppercase

strrev: String reversal (only English can be reversed: English storage has only one byte), reversed according to bytes

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

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

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: from 1970 Greenwich Mean Time Number of seconds starting at 0:00:00 on January 1st

date: Time serialization function, converts the specified timestamp into the specified time and date display format (arbitrary string: professional format Requirements), if no timestamp is specified, the system defaults to the timestamp of the current time

strtotime: A string in the time and date format is converted into the corresponding timestamp (as long as it is a correct English time expression, any Convert)

microtime: microsecond timestamp, returns different results according to different requirements Mixed microtime (Boolean type), can return a floating point number of time, or can return an array (timestamp and microseconds Number)

Mathematical related functions

abs: absolute value

floor: round down floor(3.2) 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 (efficiency Higher)

Array related functions

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

current: Get the current pointer The value pointing to the element

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

prev: Get the value of the previous element and move the pointer up

end: Move the pointer to the last element of the array and return the value of the final pointer position

reset: Move the pointer to the first element of the array and return the value of the final pointer position

array_keys: Get all the key names of an array, return an index array

array_values: Get all the values ​​of an array, return an index array

explode: Explode, will A string divides the array 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: Glue, combine an array All elements inside are spliced ​​into a string according to a specified rule (special characters)

array_merge: Merge refers to accumulating the elements in two arrays. 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：Judge integer type

is_object：Judge object

is_array：Judge array

is_string：Judge string

is_resource：Judge resource

is_scalar: scalar is scalar, the judgment is basic Data type: integer, floating point, Boolean and string type

is_null: whether it is empty

is_numeric: Determine numbers or strings composed of pure numbers

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 current resource pointer from the folder resource The name of the pointed file, the pointer will move downward one bit

closedir (resource): release the corresponding file resource

scandir (path): read all file names inside a path, Returns 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 whether a specified path is a file (file)

mkdir: Create a path, if the path exists Error

rmdir: Remove folder

file_get_contents: Read data content from a specified file.

file_put_contents: Write the specified string to the corresponding file

fopen: Open a file resource

fgetc: c represents character, once Read a character

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 operate on the current resource pointer, and will move the pointer down after reading.

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

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

fseek: Specify the pointer to the corresponding position

fclose: Use the corresponding File resources

copy: copy

unlink: delete file

rename: rename file

filemtime: m represents modify, the file was last modified Time

filesize: File size (bytes)

fileperms: File permissions (octal under Linux)

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