A complete list of commonly used system functions in PHP

String function

strlen: Get the string length, byte length

substr_count The number of times a certain string appears

substr: character String interception, obtain the string (interception according to bytes)

mb_strlen
mb_substr

strchr: similar to substr, intercept from the specified position to the end

strrchr (Get 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 reversal (only English can be reversed: English storage only has one byte), reverse by byte

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 space

str_split function splits a string into an array.

chunk_split() function splits the string into a series of smaller parts

str_repeat("Shanghai",5);Repeat the string "Shanghai " 5 times

str_replace('\\', '/', dirname(DIR))); Replace

ucfirst capitalize the first letter

Time and date function

time: get the current time Timestamp (integer: starting from 0:00:00 on January 1, 1970, Greenwich Mean Time) Number of seconds

date: Time serialization function, converts the specified timestamp into the specified time and date Display format (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 into the corresponding time Stamp (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 number Time, you can also return an array (timestamp and microseconds)

Mathematical related functions

abs: absolute value

floor: round down floor(3.2) The result is equal to 3

ceil: round up

round: round up

rand: get a random integer within the specified range

mt_rand: get a specified Random integer in the range (more efficient)

min: PHP will treat non-numeric strings as 0, but if this is the smallest value, it will still return a string. If multiple parameters evaluate to 0 and are the minimum value, min() will return the smallest string in alphabetical order, or 0 of the value if there is no string;

max:PHP Non-numeric strings will be treated as 0, but if this is the largest value, a string will still be returned. If multiple arguments evaluate to 0 and are the maximum value, max() returns the numeric 0 among them, or the alphabetically largest string if there are no numeric 0s in the arguments. For multiple arrays, max is compared from left to right; if array and non-array parameters appear at the same time, the array is always returned as the maximum value;

Array related functions

count() // Non-array Return 1

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

current: Get the value of the element pointed to by the current pointer

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 last element of the array The first element, returns the value of the final pointer position

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

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

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

split is similar to explode. explode('.', 'abc.txt') is equal to split('\.', 'abc.txt')

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

join() combines array elements into a string

array_merge: Merging refers to accumulating 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.

array_reverse — Returns the reversed array

array_flip — Swaps the keys and values ​​in the array

Data structure simulation function

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

array_pop: Pop elements from the back of the array to 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

Judgment 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：Judge object

is_array：Judge array

is_string：Judge string

is_resource: Determine the resource

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

is_null detects whether the variable is NULL and returns TRUE otherwise returns false. 1. Being assigned a value of NULL; 2. The variable has not been assigned a value; 3. Being unset()

is_numeric: Determine a string composed of numbers or pure numbers

gettype : Get the data type

settype: Change the data type

isset

unset() if in the function unset() is a global variable, only the local variable is destroyed, and the variables in the calling environment will keep the same value before calling unset(). If unset() is passed in the function Quoting the variable passed , only the local variable is destroyed, and the variable in the calling environment will maintain the same value before calling unset().
empty//array(),"",0,"0",NULL,FALSE all return true

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 the 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 (file folder)

is_file: Determine whether a specified path is a file (file)

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

rmdir：Remove the folder

file_get_contents: Read the 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, read one character at a time

fgets： s stands for string, which means multiple characters can be read, depending on the specified read length or whether a newline is encountered (up to Get a row of data)

Both functions operate on the current resource pointer. After reading, the pointer will be moved down.

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

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

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 (words Section)

fileperms: File permissions (octal under Linux)

Sorting

rsort() function is used to sort array cells from high to low.
asort() function is used to sort the array cells from low to high and maintain the index relationship.
arsort() function is used to sort the array cells from high to low and maintain the index relationship.
ksort() function is used to sort array cells from low to high by key name.
krsort() function is used to sort array cells from high to low by key name.

Error reporting

error_reporting(E_ALL)

ini_set('display_errors', 1)

Constant

define() Define constant
defined() Check whether the constant is defined

Serialize

serialize

unserialize

json_encode JSON encode the variable

json_decode Encoding a string in JSON format

Encoding

base64_encode This function encodes the string in MIME BASE64. The string encoded by BASE64 only contains uppercase and lowercase English letters, Arabic numerals, plus signs and backslashes, a total of 64 basic characters, and does not contain other special characters, so it is named BASE64.

base64_decode decoding

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