Commonly used system functions in php projects

String function

strlen: Get the string length, byte length

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

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: English storage has only one byte) , reverse by bytes

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

strrpos: Same as strpos, except from Start looking for the right side of the string

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

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, can also return an array (timestamp and microseconds)

Mathematical related functions

abs: absolute value

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

ceil: Round up

round: Rounding

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 next element pointed to by the current pointer of the current array Standard

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 value, 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 , 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 in an array into a string according to a specified rule (special characters)

array_merge: Merging, refers to combining the elements in two arrays Elements 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 the 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 (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: From a specified Read the data content in the 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 the length or encounter a newline (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 data of the specified length until the end of the file

fwrite: Write data to the location of the file resource pointer. 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 the file

rename: Rename the file

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

filesize: file size (bytes)

fileperms: file permissions (under Linux octal)