Language support Digraphs and trigraphs

-



1 language support

1.1 algol
1.2 pascal
1.3 vim
1.4 gnu screen
1.5 j
1.6 c
1.7 c++

1.7.1 removal of trigraphs


1.8 rpl





language support

different systems define different sets of digraphs , trigraphs, described below.


algol

early versions of algol predated standardised ascii , ebcdic character sets, , typically implemented using manufacturer-specific six-bit character code. number of algol operations either lacked codepoints in available character set or not supported peripherals, leading number of substitutions including := ← (assignment) , >= ≥ (greater or equal).


pascal

pascal programming language supports digraphs (., .), (* , *) [, ], { , } respectively. unlike other cases mentioned here, (* , *) , still in wide use.


vim

vim text editor supports digraphs actual entry of text characters, following rfc 1345.


gnu screen

gnu screen has digraph command, bound ^a ^v default.


j

the j programming language descendant of apl using ascii character set rather traditional apl symbols. handle fact printable range of ascii smaller apl s specialised set of symbols, . (dot) , : (colon) characters used inflect ascii symbols, interpreting unigraphs, digraphs or trigraphs standalone symbols .


unlike use of digraphs , trigraphs in c , c++, there no single-character equivalents these in j.


c

the c preprocessor replaces occurrences of following 9 trigraph sequences single-character equivalents before other processing.



a programmer may want place 2 question marks yet not have compiler treat them introducing trigraph. c grammar not permit 2 consecutive ? tokens, places in c file 2 question marks in row may used in multi-character constants, string literals, , comments. particularly problem classic mac os, constant ???? may used file type or creator. safely place 2 consecutive question marks within string literal, programmer can use string concatenation ...? ?... or escape sequence ...?\?... .


??? not trigraph sequence, when followed character such - interpreted ? + ??-, in example below has 16 ?s before /.


the ??/ trigraph can used introduce escaped newline line splicing; must taken account correct , efficient handling of trigraphs within preprocessor. can cause surprises, particularly within comments. example:



// next line executed????????????????/
a++;

which single logical comment line (used in c++ , c99), and



/??/
* comment *??/
/

which correctly formed block comment.



in 1994, normative amendment c standard, included in c99, supplied digraphs more readable alternatives 5 of trigraphs. listed in table on right.


unlike trigraphs, digraphs handled during tokenization, , digraph must represent full token itself, or compose token %:%: replacing preprocessor concatenation token ##. if digraph sequence occurs inside token, example quoted string, or character constant, not replaced.



c++

c++ (through c++14, see below) behaves c, including c99 additions, additional tokens listed in table.


as note, %:%: treated single token, rather 2 occurrences of %:.


the c++ standard makes comment regards term digraph :



the term digraph (token consisting of 2 characters) not descriptive, since 1 of alternative preprocessing-tokens %:%: , of course several primary tokens contain 2 characters. nonetheless, alternative tokens aren’t lexical keywords colloquially known digraphs .




removal of trigraphs

trigraphs proposed deprecation in c++0x, released c++11. opposed ibm, speaking on behalf of , other users of c++, , result trigraphs retained in c++0x. trigraphs proposed again removal (not deprecation) in c++17. passed committee vote, , trigraphs removed c++17 despite opposition ibm. existing code uses trigraphs can supported translating source files (parsing trigraphs) basic source character set not include trigraphs.


rpl

hewlett-packard calculators supporting rpl language , input method provide support large number of trigraphs (also called tio codes) reliably transcribe non-seven-bit ascii characters of calculators extended character set on foreign platforms, , ease keyboard input without using chars application.









Comments

Post a Comment

Popular posts from this blog

Weir report (2001) Rotherham child sexual exploitation scandal

-
1 weir report (2001) 1.1 home office pilot study 1.2 mapping exercise 1.3 home office report 1.4 files removed weir report (2001) home office pilot study in 2000 adele weir (later gladman), yorkshire solicitor, hired rotherham council research , development officer on home office crime reduction programme pilot study, tackling prostitution: works . section of study devoted young people , prostitution , , 3 towns—bristol, sheffield , rotherham—were highlighted in section. weir employed write report on rotherham. part of project s aim was: collection of information , evidence men allegedly involved in coercing young women prostitution might possible police pursue investigations and/or prosecutions. researchers @ university of bedfordshire, including social scientist margaret melrose, involved home office evaluators. weir s line manager manager of risky business, , placed in risky business offices in rotherham s international centre, worked jayne senior. according weir, encountered po...
Read more

Mussolini's views on antisemitism and race Benito Mussolini

-
mussolini adolf hitler in berlin, 1937 although mussolini had disregarded biological racism, firm believer in national traits , made several generalizations jews. nevertheless, mussolini considered italian jews italians. mussolini s antisemitic remarks in late 1910s , 1920s more suited moment rather sincere belief in them. mussolini blamed russian revolution of 1917 on jewish vengeance against christianity remark race not betray race . . . bolshevism being defended international plutocracy. real truth. yet within few weeks did u-turn remark bolshevism not, people believe, jewish phenomenon. truth bolshevism leading utter ruin of jews of eastern europe. in 1920s, mussolini stated fascism never raise jewish question , in article wrote stated italy knows no antisemitism , believe never know it. , elaborated let hope italian jews continue sensible enough not give rise antisemitism in country has never existed. in 1932, mussolini during conversation emil ludwig described antisemi...
Read more

Types Classification yard

-
1 types 1.1 flat yard 1.2 hump yard 1.3 gravity yard types flat yard flat yards constructed on flat ground, or on gentle slope. freight cars pushed locomotive , coast required location. cnw towerman r. w. mayberry operates retarders @ proviso yard in chicago, illinois, may 1943. hump yard not cars can sent on classification hump. union pacific track maintenance vehicle permanently labelled not hump , because not designed withstand hump sorting. hump yards largest , effective classification yards, largest shunting capacity, several thousand cars day. heart of these yards hump—a lead track on small hill on engine pushes cars. single cars, or block of coupled cars, uncoupled before or @ crest of hump, , roll gravity onto destination tracks in tracks cars sorted, called classification bowl. the speed of cars rolling down hump classification bowl must regulated according whether full or empty, heavy or light freight, varying number of axles, whether there few or many cars on classification...
Read more