目录
- PHP 教程
- PHP 表单
- PHP 高级
- PHP 面向对象编程
- MySQL 数据库
- PHP XML
- PHP - AJAX
- PHP 示例
-
PHP 参考
- PHP 概述
-
PHP 数组
- PHP 数组
- array()
- array_change_key_case()
- array_chunk()
- array_column()
- array_combine()
- array_count_values()
- array_diff()
- array_diff_assoc()
- array_diff_key()
- array_diff_uassoc()
- array_diff_ukey()
- array_fill()
- array_fill_keys()
- array_filter()
- array_flip()
- array_intersect()
- array_intersect_assoc()
- array_intersect_key()
- array_intersect_uassoc()
- array_intersect_ukey()
- array_key_exists()
- array_keys()
- array_map()
- array_merge()
- array_merge_recursive()
- array_multisort()
- array_pad()
- array_pop()
- array_product()
- array_push()
- array_rand()
- array_reduce()
- array_replace()
- array_replace_recursive()
- array_reverse()
- array_search()
- array_shift()
- array_slice()
- array_splice()
- array_sum()
- array_udiff()
- array_udiff_assoc()
- array_udiff_uassoc()
- array_uintersect()
- array_uintersect_assoc()
- array_uintersect_uassoc()
- array_unique()
- array_unshift()
- array_values()
- array_walk()
- array_walk_recursive()
- arsort()
- asort()
- compact()
- count()
- current()
- each()
- end()
- extract()
- in_array()
- key()
- krsort()
- ksort()
- list()
- natcasesort()
- natsort()
- next()
- pos()
- prev()
- range()
- reset()
- rsort()
- shuffle()
- sizeof()
- sort()
- uasort()
- uksort()
- usort()
- PHP 日历
-
PHP 日期
- PHP 日期
- checkdate()
- date_add()
- date_create_from_format()
- date_create()
- date_date_set()
- date_default_timezone_get()
- date_default_timezone_set()
- date_diff()
- date_format()
- date_get_last_errors()
- date_interval_create_from_date_string()
- date_interval_format()
- date_isodate_set()
- date_modify()
- date_offset_get()
- date_parse_from_format()
- date_parse()
- date_sub()
- date_sun_info()
- date_sunrise()
- date_sunset()
- date_time_set()
- date_timestamp_get()
- date_timestamp_set()
- date_timezone_get()
- date_timezone_set()
- date()
- getdate()
- gettimeofday()
- gmdate()
- gmmktime()
- gmstrftime()
- idate()
- localtime()
- microtime()
- mktime()
- strftime()
- strptime()
- strtotime()
- time()
- timezone_abbreviations_list()
- timezone_identifiers_list()
- timezone_location_get()
- timezone_name_from_abbr()
- timezone_name_get()
- timezone_offset_get()
- timezone_open()
- timezone_transitions_get()
- timezone_version_get()
- PHP 目录
- PHP 错误
- PHP 异常
-
PHP 文件系统
- PHP 文件系统
- basename()
- chgrp()
- chmod()
- chown()
- clearstatcache()
- copy()
- delete()
- dirname()
- disk_free_space()
- disk_total_space()
- diskfreespace()
- fclose()
- feof()
- fflush()
- fgetc()
- fgetcsv()
- fgets()
- fgetss()
- file()
- file_exists()
- file_get_contents()
- file_put_contents()
- fileatime()
- filectime()
- filegroup()
- fileinode()
- filemtime()
- fileowner()
- fileperms()
- filesize()
- filetype()
- flock()
- fnmatch()
- fopen()
- fpassthru()
- fputcsv()
- fputs()
- fread()
- fscanf()
- fseek()
- fstat()
- ftell()
- ftruncate()
- fwrite()
- glob()
- is_dir()
- is_executable()
- is_file()
- is_link()
- is_readable()
- is_uploaded_file()
- is_writable()
- is_writeable()
- lchgrp()
- lchown()
- link()
- linkinfo()
- lstat()
- mkdir()
- move_uploaded_file()
- parse_ini_file()
- parse_ini_string()
- pathinfo()
- pclose()
- popen()
- readfile()
- readlink()
- realpath()
- realpath_cache_get()
- realpath_cache_size()
- rename()
- rewind()
- rmdir()
- set_file_buffer()
- stat()
- symlink()
- tempnam()
- tmpfile()
- touch()
- umask()
- unlink()
- PHP 过滤器
-
PHP FTP
- PHP FTP
- ftp_alloc()
- ftp_cdup()
- ftp_chdir()
- ftp_chmod()
- ftp_close()
- ftp_connect()
- ftp_delete()
- ftp_exec()
- ftp_fget()
- ftp_fput()
- ftp_get()
- ftp_get_option()
- ftp_login()
- ftp_mdtm()
- ftp_mkdir()
- ftp_mlsd()
- ftp_nb_continue()
- ftp_nb_fget()
- ftp_nb_fput()
- ftp_nb_get()
- ftp_nb_put()
- ftp_nlist()
- ftp_pasv()
- ftp_put()
- ftp_pwd()
- ftp_quit()
- ftp_raw()
- ftp_rawlist()
- ftp_rename()
- ftp_rmdir()
- ftp_set_option()
- ftp_site()
- ftp_size()
- ftp_ssl_connect()
- ftp_systype()
- PHP JSON
-
PHP 关键字
- PHP 关键字
- abstract
- and
- as
- break
- callable
- case
- catch
- class
- clone
- const
- continue
- declare
- default
- do
- echo
- else
- elseif
- empty
- enddeclare
- endfor
- endforeach
- endif
- endswitch
- extends
- final
- finally
- fn
- for
- foreach
- function
- global
- if
- implements
- include
- include_once
- instanceof
- insteadof
- interface
- isset
- list
- namespace
- new
- or
- private
- protected
- public
- require
- require_once
- return
- static
- switch
- throw
- trait
- try
- use
- var
- while
- xor
- yield
- yield from
- PHP Libxml
- PHP 邮件
-
PHP 数学
- PHP 数学
- abs()
- acos()
- acosh()
- asin()
- asinh()
- atan()
- atan2()
- atanh()
- base_convert()
- bindec()
- ceil()
- cos()
- cosh()
- decbin()
- dechex()
- decoct()
- deg2rad()
- exp()
- expm1()
- floor()
- fmod()
- getrandmax()
- hexdec()
- hypot()
- intdiv()
- is_finite()
- is_infinite()
- is_nan()
- lcg_value()
- log()
- log10()
- log1p()
- max()
- min()
- mt_getrandmax()
- mt_rand()
- mt_srand()
- octdec()
- pi()
- pow()
- rad2deg()
- rand()
- round()
- sin()
- sinh()
- sqrt()
- srand()
- tan()
- tanh()
-
PHP 杂项
- PHP 杂项
- connection_aborted()
- connection_status()
- connection_timeout()
- constant()
- define()
- defined()
- die()
- eval()
- exit()
- get_browser()
- __halt_compiler()
- highlight_file()
- highlight_string()
- hrtime()
- ignore_user_abort()
- pack()
- php_strip_whitespace()
- show_source()
- sleep()
- sys_getloadavg()
- time_nanosleep()
- time_sleep_until()
- uniqid()
- unpack()
- usleep()
-
PHP MySQLi
- PHP MySQLi
- affected_rows
- autocommit
- change_user
- character_set_name
- close
- commit
- connect
- connect_errno
- connect_error
- data_seek
- debug
- dump_debug_info
- errno
- error
- error_list
- fetch_all
- fetch_array
- fetch_assoc
- fetch_field
- fetch_field_direct
- fetch_fields
- fetch_lengths
- fetch_object
- fetch_row
- field_count
- field_seek
- get_charset
- get_client_info
- get_client_stats
- get_client_version
- get_connection_stats
- get_host_info
- get_proto_info
- get_server_info
- get_server_version
- info
- init
- insert_id
- kill
- more_results
- multi_query
- next_result
- options
- ping
- poll
- prepare
- query
- real_connect
- real_escape_string
- real_query
- reap_async_query
- refresh
- rollback
- select_db
- set_charset
- set_local_infile_handler
- sqlstate
- ssl_set
- stat
- stmt_init
- thread_id
- thread_safe
- use_result
- warning_count
-
PHP 网络
- PHP 网络
- checkdnsrr()
- closelog()
- dns_check_record()
- dns_get_mx()
- dns_get_record()
- fsockopen()
- gethostbyaddr()
- gethostbyname()
- gethostbynamel()
- gethostname()
- getmxrr()
- getprotobyname()
- getprotobynumber()
- getservbyname()
- getservbyport()
- header_register_callback()
- header_remove()
- header()
- headers_list()
- headers_sent()
- http_response_code()
- inet_ntop()
- inet_pton()
- ip2long()
- long2ip()
- openlog()
- pfsockopen()
- setcookie()
- setrawcookie()
- socket_get_status()
- socket_set_blocking()
- socket_set_timeout()
- syslog()
- PHP 输出控制
- PHP 正则表达式
-
PHP SimpleXML
- PHP SimpleXML
- __construct()
- __tostring()
- addAttribute()
- addChild()
- asXML()
- attributes()
- children()
- count()
- getDocNamespaces()
- getName()
- getNamespaces()
- registerXPathNamespace()
- saveXML()
- simplexml_import_dom()
- simplexml_load_file()
- simplexml_load_string()
- xpath()
- current()
- getchildren()
- haschildren()
- key()
- next()
- rewind()
- valid()
- PHP 流
-
PHP 字符串
- PHP 字符串
- addcslashes()
- addslashes()
- bin2hex()
- chop()
- chr()
- chunk_split()
- convert_cyr_string()
- convert_uudecode()
- convert_uuencode()
- count_chars()
- crc32()
- crypt()
- echo()
- explode()
- fprint()
- get_html_translation_table()
- hebrev()
- hebrevc()
- hex2bin()
- html_entity_decode()
- htmlentities()
- htmlspecialchars_decode()
- htmlspecialchars()
- implode()
- join()
- lcfirst()
- levenshtein()
- localeconv()
- ltrim()
- md5()
- md5_file()
- metaphone()
- money_format()
- nl_langinfo()
- nl2br()
- number_format()
- ord()
- parse_str()
- print()
- printf()
- quoted_printable_decode()
- quoted_printable_encode()
- quotemeta()
- rtrim()
- setlocale()
- sha1()
- sha1_file()
- similar_text()
- soundex()
- sprintf()
- sscanf()
- str_getcsv()
- str_ireplace()
- str_pad()
- str_repeat()
- str_replace()
- str_rot13()
- str_shuffle()
- str_split()
- str_word_count()
- strcasecmp()
- strchr()
- strcmp()
- strcoll()
- strcspn()
- strip_tags()
- stripcslashes()
- stripslashes()
- stripos()
- stristr()
- strlen()
- strnatcasecmp()
- strnatcmp()
- strncasecmp()
- strncmp()
- strpbrk()
- strpos()
- strrchr()
- strrev()
- strripos()
- strrpos()
- strspn()
- strstr()
- strtok()
- strtolower()
- strtoupper()
- strtr()
- substr()
- substr_compare()
- substr_count()
- substr_replace()
- trim()
- ucfirst()
- ucwords()
- vfprintf()
- vprintf()
- vsprintf()
- wordwrap()
-
PHP 变量处理
- PHP 变量处理
- boolval()
- debug_zval_dump()
- doubleval()
- is_countable()
- empty()
- floatval()
- get_defined_vars()
- get_resource_type()
- gettype()
- intval()
- is_array()
- is_bool()
- is_callable()
- is_double()
- is_float()
- is_int()
- is_integer()
- is_iterable()
- is_long()
- is_null()
- is_numeric()
- is_object()
- is_real()
- is_resource()
- is_scalar()
- is_string()
- isset()
- print_r()
- serialize()
- settype()
- strval()
- unserialize()
- unset()
- var_dump()
- var_export()
-
PHP XML解析器
- PHP XML解析器
- utf8_decode()
- utf8_encode()
- xml_error_string()
- xml_get_current_byte_index()
- xml_get_current_column_number()
- xml_get_current_line_number()
- xml_get_error_code()
- xml_parse()
- xml_parse_into_struct()
- xml_parser_create_ns()
- xml_parser_create()
- xml_parser_free()
- xml_parser_get_option()
- xml_parser_set_option()
- xml_set_character_data_handler()
- xml_set_default_handler()
- xml_set_element_handler()
- xml_set_end_namespace_decl_handler()
- xml_set_external_entity_ref_handler()
- xml_set_notation_decl_handler()
- xml_set_object()
- xml_set_processing_instruction_handler()
- xml_set_start_namespace_decl_handler()
- xml_set_unparsed_entity_decl_handler()
- PHP Zip
- PHP 时区
PHP defined() 函数
示例
检查常量是否存在：
<?php
define("GREETING","Hello you! How are you today?");
echo defined("GREETING");
?>
亲自试一试 »
定义和用法
Defined() 函数检查常量是否存在。
语法
defined(
name)
参数值
| Parameter | Description |
|---|---|
| name | Required. Specifies the name of the constant to check |
技术细节
| 返回值： | 如果常量存在则返回 TRUE，否则返回 FALSE |
|---|---|
| PHP 版本： | 4+ |
❮ PHP 其他参考
截取页面反馈部分，让我们更快修复内容！也可以直接跳过填写反馈内容!