A reserved word in a programming language is a word that is off limits to the programmer. For example, in PHP print is a reserved word. This means that you, as the programmer, cannot create a function named print because PHP owns that word.
Most languages have reserved words, some a few, and some very, very many. Usually the fewer reserved words a language has, the more flexible it is. For example, in the list below, you will see that Lisp has no reserved words. We all know that Lisp is very flexible and powerful.
As you look at the table below, do not think unkind thoughts about PHP—it’s different from the other languages. It is not designed to be a general purpose programming language, though it can certainly do almost anything you want it to do. It is intended for web programming, which explains the existence of so many of the predefined functions and constants. Those are exactly the kinds of items that other languages must implement individually if they want to be as handy with web development as PHP. This is no small task, kids. Just take a look around try to find a web site implemented in C++.
Reserved Words
| Language | Count | Reserved Words |
|---|---|---|
| Lisp | 0 | Lisp has no reserved words. Lisp is written in Lisp. Alan Kay, the creator of Smalltalk, said: “Lisp isn’t a language, it’s a building material.” |
| Smalltalk | 5 | self super nil true false |
| C | 32 | auto break case chart const continue default do double else enum extern float for goto if int long register return short signed sizeof static struct switch typedef union unsigned void volatile while |
| C++ | ~62 | and and_eq asm auto bitand bitor bool break case catch char class compl const const_cast continue default delete do double dynamic_cast else enum explicit export extern false float for friend goto if inline int long mutable namespace new not not_eq operator or or_eq private protected public register reinterpret_cast return short signed sizeof static static_cast struct switch template this throw true try typedef typeid typename union unsigned using virtual void volatile wchar_t while xor xor_eq |
| Ruby | 38 | alias and BEGIN begin break case class def defined? do else elsif END end ensure false for if in module next nil not or redo rescue retry return self super then true undef unless until when while yield |
| Python | 31 | and del from not while as elif global or with assert else if pass yield break except import print class exec in raise continue finally is return def for lambda try |
| Java | 47 | abstract do if package synchronized boolean double implements private this break else import protected throw byte extends instanceof public throws case false int return transient catch final interface short true char finally long static try class float native strictfp void const for new super volatile continue goto null switch while default assert |
| PHP | 418 | __CLASS__ __COMPILER_HALT_OFFSET__ __FILE__ __FUNCTION__ __LINE__ __METHOD__ __PHP_INCOMPLETE_CLASS ABDAY_1 ABDAY_2 ABDAY_3 ABDAY_4 ABDAY_5 ABDAY_6 ABDAY_7 ABMON_1 ABMON_10 ABMON_11 ABMON_12 ABMON_2 ABMON_3 ABMON_4 ABMON_5 ABMON_6 ABMON_7 ABMON_8 ABMON_9 ABSTRACT ALT_DIGITS AM_STR AND ARGC ARGV ARRAY AS ASSERT_ACTIVE ASSERT_BAIL ASSERT_CALLBACK ASSERT_QUIET_EVAL ASSERT_WARNING AUTH_TYPE BREAK CASE CASE_LOWER CASE_UPPER CATCH CFUNCTION CHAR_MAX CLASS CLONE CODESET CONNECTION_ABORTED CONNECTION_NORMAL CONNECTION_TIMEOUT CONST CONTINUE COUNT_NORMAL COUNT_RECURSIVE CREDITS_ALL CREDITS_DOCS CREDITS_FULLPAGE CREDITS_GENERAL CREDITS_GROUP CREDITS_MODULES CREDITS_QA CREDITS_SAPI CRNCYSTR CRYPT_BLOWFISH CRYPT_EXT_DES CRYPT_MD5 CRYPT_SALT_LENGTH CRYPT_STD_DES CURRENCY_SYMBOL D_FMT D_T_FMT DAY_1 DAY_2 DAY_3 DAY_4 DAY_5 DAY_6 DAY_7 DECIMAL_POINT DECLARE DEFAULT DEFAULT_INCLUDE_PATH DIE DIRECTORY_SEPARATOR DO DOCUMENT_ROOT E_ALL E_COMPILE_ERROR E_COMPILE_WARNING E_CORE_ERROR E_CORE_WARNING E_ERROR E_NOTICE E_PARSE E_STRICT E_USER_ERROR E_USER_NOTICE E_USER_WARNING E_WARNING ECHO ELSE ELSEIF EMPTY ENDDECLARE ENDFOR ENDFOREACH ENDIF ENDSWITCH ENDWHILE ENT_COMPAT ENT_NOQUOTES ENT_QUOTES ERA ERA_D_FMT ERA_D_T_FMT ERA_T_FMT ERA_YEAR EVAL EXCEPTION EXIT EXTENDS EXTR_IF_EXISTS EXTR_OVERWRITE EXTR_PREFIX_ALL EXTR_PREFIX_IF_EXISTS EXTR_PREFIX_INVALID EXTR_PREFIX_SAME EXTR_SKIP FINAL FOR FOREACH FRAC_DIGITS FUNCTION GATEWAY_INTERFACE GLOBAL GROUPING HTML_ENTITIES HTML_SPECIALCHARS HTTP_ACCEPT HTTP_ACCEPT_CHARSET HTTP_ACCEPT_ENCODING HTTP_ACCEPT_LANGUAGE HTTP_CONNECTION HTTP_HOST HTTP_REFERER HTTP_USER_AGENT HTTPS IF IMPLEMENTS INCLUDE INCLUDE_ONCE INFO_ALL INFO_CONFIGURATION INFO_CREDITS INFO_ENVIRONMENT INFO_GENERAL INFO_LICENSE INFO_MODULES INFO_VARIABLES INI_ALL INI_PERDIR INI_SYSTEM INI_USER INT_CURR_SYMBOL INT_FRAC_DIGITS INTERFACE ISSET LC_ALL LC_COLLATE LC_CTYPE LC_MESSAGES LC_MONETARY LC_NUMERIC LC_TIME LIST LOCK_EX LOCK_NB LOCK_SH LOCK_UN LOG_ALERT LOG_AUTH LOG_AUTHPRIV LOG_CONS LOG_CRIT LOG_CRON LOG_DAEMON LOG_DEBUG LOG_EMERG LOG_ERR LOG_INFO LOG_KERN LOG_LOCAL0 LOG_LOCAL1 LOG_LOCAL2 LOG_LOCAL3 LOG_LOCAL4 LOG_LOCAL5 LOG_LOCAL6 LOG_LOCAL7 LOG_LPR LOG_MAIL LOG_NDELAY LOG_NEWS LOG_NOTICE LOG_NOWAIT LOG_ODELAY LOG_PERROR LOG_PID LOG_SYSLOG LOG_USER LOG_UUCP LOG_WARNING M_1_PI M_2_PI M_2_SQRTPI M_E M_LN10 M_LN2 M_LOG10E M_LOG2E M_PI M_PI_2 M_PI_4 M_SQRT1_2 M_SQRT2 MON_1 MON_10 MON_11 MON_12 MON_2 MON_3 MON_4 MON_5 MON_6 MON_7 MON_8 MON_9 MON_DECIMAL_POINT MON_GROUPING MON_THOUSANDS_SEP N_CS_PRECEDES N_SEP_BY_SPACE N_SIGN_POSN NEGATIVE_SIGN NEW NOEXPR NOSTR OLD_FUNCTION OR P_CS_PRECEDES P_SEP_BY_SPACE P_SIGN_POSN PATH_SEPARATOR PATH_TRANSLATED PATHINFO_BASENAME PATHINFO_DIR NAME PATHINFO_EXTENSION PEAR_EXTENSION_DIR PEAR_INSTALL_DIR PHP_AUTH_DIGEST PHP_AUTH_PW PHP_AUTH_USER PHP_BINDIR PHP_CONFIG_FILE_PATH PHP_CONFIG_FILE_SCAN_DIR PHP_DATADIR PHP_EOL PHP_EXTENSION_DIR PHP_INT_MAX PHP_INT_SIZE PHP_LIBDIR PHP_LOCALSTATEDIR PHP_OS PHP_OUTPUT_HANDLER_CONT PHP_OUTPUT_HANDLER_END PHP_OUTPUT_HANDLER_START PHP_PREFIX PHP_SAPI PHP_SELF PHP_SHLIB_SUFFIX PHP_SYSCONFDIR PHP_USER_FILTER PHP_USER_FILTER PHP_VERSION PM_STR POSITIVE_SIGN PRINT PRIVATE PROTECTED PUBLIC QUERY_STRING RADIXCHAR REMOTE_ADDR REMOTE_HOST REMOTE_PORT REQUEST_METHOD REQUEST_TIME REQUEST_URI REQUIRE REQUIRE_ONCE RETURN SCRIPT_FILENAME SCRIPT_NAME SEEK_CUR SEEK_END SEEK_SET SERVER_ADDR SERVER_ADMIN SERVER_NAME SERVER_PORT SERVER_PROTOCOL SERVER_SIGNATURE SERVER_SOFTWARE SORT_ASC SORT_DESC SORT_NUMERIC SORT_REGULAR SORT_STRING STATIC STDCLASS STR_PAD_BOTH STR_PAD_LEFT STR_PAD_RIGHT SWITCH T_FMT T_FMT_AMPM THIS THOUSANDS_SEP THOUSEP THROW TRY UNSET USE VAR WHILE XOR YESEXPR YESSTR LASS__ __COMPILER_HALT_OFFSET__ __FILE__ __FUNCTION__ __LINE__ __METHOD__ __PHP_INCOMPLETE_CLASS ABDAY_1 ABDAY_2 ABDAY_3 ABDAY_4 ABDAY_5 ABDAY_6 ABDAY_7 ABMON_1 ABMON_10 ABMON_11 ABMON_12 ABMON_2 ABMON_3 ABMON_4 ABMON_5 ABMON_6 ABMON_7 ABMON_8 ABMON_9 ABSTRACT ALT_DIGITS AM_STR AND ARGC ARGV ARRAY AS ASSERT_ACTIVE ASSERT_BAIL ASSERT_CALLBACK ASSERT_QUIET_EVAL ASSERT_WARNING AUTH_TYPE BREAK CASE CASE_LOWER CASE_UPPER CATCH CFUNCTION CHAR_MAX CLASS CLONE CODESET CONNECTION_ABORTED CONNECTION_NORMAL CONNECTION_TIMEOUT CONST CONTINUE COUNT_NORMAL COUNT_RECURSIVE CREDITS_ALL CREDITS_DOCS CREDITS_FULLPAGE CREDITS_GENERAL CREDITS_GROUP CREDITS_MODULES CREDITS_QA CREDITS_SAPI CRNCYSTR CRYPT_BLOWFISH CRYPT_EXT_DES CRYPT_MD5 CRYPT_SALT_LENGTH CRYPT_STD_DES CURRENCY_SYMBOL D_FMT D_T_FMT DAY_1 DAY_2 DAY_3 |
