1344:
22:
386:
For example, an array of 256 eight-bit integers, arranged as bitfields, is created, where each bit corresponds to a particular property of the character, e.g., isdigit, isalpha. If the lowest-order bit of the integers corresponds to the isdigit property, the code could be written as
283:. These functions are used to test characters for membership in a particular class of characters, such as alphabetic characters, control characters, etc. Both single-byte, and wide characters are supported.
383:
Unlike the above example, the character classification routines are not written as comparison tests. In most C libraries, they are written as static table lookups instead of macros or functions.
371:
As this may be expressed in multiple formulations, it became desirable to introduce short, standardized forms of such tests that were placed in the system-wide header file
871:
259:
86:
39:
58:
65:
72:
864:
1184:
54:
1348:
105:
252:
1165:
1074:
857:
1283:
416:
43:
1303:
1255:
1372:
1313:
1298:
1004:
245:
171:
79:
1260:
1308:
1014:
911:
906:
901:
161:
1288:
999:
947:
880:
280:
166:
151:
1151:
1126:
32:
1169:
1111:
829:
1131:
646:
186:
8:
1146:
1141:
1103:
994:
156:
1212:
977:
942:
767:
582:
276:
121:
752:
737:
718:
699:
680:
661:
639:
620:
601:
575:
563:
544:
525:
506:
487:
1045:
1040:
1009:
952:
800:
730:
711:
692:
673:
654:
632:
613:
594:
556:
537:
518:
499:
480:
296:
181:
176:
146:
782:
411:
This can cause problems if when the macro expands, the expression substituted for
1156:
1116:
1024:
431:
is evaluated twice. For this reason, the table-based approach is generally used.
1329:
1174:
1136:
1062:
962:
303:
character set, the following expression identifies a letter, when its value is
1366:
1232:
1222:
1161:
1202:
967:
406:#define isdigit(x) ((x) >= '0' && (x) <= '9')
136:
1293:
849:
937:
916:
447:
in C++). The functions that operate on wide characters are defined in
299:
for classifying characters into different types. For example, for the
439:
The functions that operate on single-byte characters are defined in
21:
1237:
1227:
1207:
1052:
1019:
957:
458:
The classification is evaluated according to the effective locale.
401:
used a potentially faulty method similar to the first code sample:
231:
222:
204:
921:
213:
1192:
1089:
1084:
891:
1278:
1217:
1197:
1121:
1069:
1057:
398:
300:
1079:
292:
896:
275:
is an operation provided by a group of functions in the
667:
checks whether the operand is a blank space character
758:
checks whether the operand falls into specific class
427:. It is not immediately evident that the argument to
686:
checks whether the operand is a printable character
626:
checks whether the operand is a graphical character
46:. Unsourced material may be challenged and removed.
607:checks whether the operand is a control character
806:returns a transformation mapping to be used with
1364:
788:returns a wide character class to be used with
773:converts the operand using a specific mapping
865:
253:
291:Early C-language programmers working on the
550:checks whether the operand is an uppercase
493:checks whether the operand is alphanumeric
879:
872:
858:
705:checks whether the operand is punctuation
588:checks whether the operand is hexadecimal
260:
246:
512:checks whether the operand is alphabetic
106:Learn how and when to remove this message
531:checks whether the operand is lowercase
434:
1365:
569:checks whether the operand is a digit
853:
44:adding citations to reliable sources
15:
13:
743:converts the operand to uppercase
724:converts the operand to lowercase
392:#define isdigit(x) (TABLE & 1)
14:
1384:
845:
378:
1343:
1342:
795:
777:
762:
747:
20:
831:ISO/IEC 9899:1999 specification
31:needs additional citations for
822:
645:checks whether the operand is
1:
815:
419:. For example, if one calls
55:"C character classification"
7:
425:isdigit(run_some_program())
295:operating system developed
10:
1389:
1256:Compatibility of C and C++
286:
273:C character classification
1338:
1322:
1269:
1246:
1183:
1102:
1033:
985:
976:
930:
887:
403:
389:
309:
142:Character classification
277:ANSI C Standard Library
1261:Comparison with Pascal
881:C programming language
281:C programming language
435:Overview of functions
195:Miscellaneous headers
40:improve this article
1373:C standard library
397:Early versions of
297:programming idioms
187:Alternative tokens
122:C standard library
1358:
1357:
1098:
1097:
813:
812:
270:
269:
172:Memory allocation
157:File input/output
116:
115:
108:
90:
1380:
1346:
1345:
983:
982:
978:Standard library
874:
867:
860:
851:
850:
839:
838:
837:. p. 193, § 7.4.
836:
826:
809:
803:
791:
785:
770:
755:
740:
733:
721:
714:
702:
695:
683:
676:
664:
657:
642:
635:
623:
616:
604:
597:
585:
578:
566:
559:
547:
540:
528:
521:
509:
502:
490:
483:
461:
460:
407:
393:
367:
364:
361:
358:
355:
352:
349:
346:
343:
340:
337:
334:
331:
328:
325:
322:
319:
316:
313:
262:
255:
248:
235:
226:
217:
208:
118:
117:
111:
104:
100:
97:
91:
89:
48:
24:
16:
1388:
1387:
1383:
1382:
1381:
1379:
1378:
1377:
1363:
1362:
1359:
1354:
1334:
1318:
1271:
1265:
1249:other languages
1248:
1247:Comparison with
1242:
1179:
1117:Borland Turbo C
1094:
1034:Implementations
1029:
972:
926:
883:
878:
848:
843:
842:
834:
828:
827:
823:
818:
807:
799:
789:
781:
766:
751:
736:
729:
717:
710:
698:
691:
679:
672:
660:
653:
638:
631:
619:
612:
600:
593:
581:
574:
562:
555:
543:
536:
524:
517:
505:
498:
486:
479:
470:
465:
437:
409:
408:
405:
395:
394:
391:
381:
369:
368:
365:
362:
359:
356:
353:
350:
347:
344:
341:
338:
335:
332:
329:
326:
323:
320:
317:
314:
311:
289:
266:
229:
220:
211:
202:
177:Process control
112:
101:
95:
92:
49:
47:
37:
25:
12:
11:
5:
1386:
1376:
1375:
1356:
1355:
1353:
1352:
1339:
1336:
1335:
1333:
1332:
1330:Dennis Ritchie
1326:
1324:
1320:
1319:
1317:
1316:
1311:
1306:
1301:
1296:
1291:
1286:
1281:
1275:
1273:
1267:
1266:
1264:
1263:
1258:
1252:
1250:
1244:
1243:
1241:
1240:
1235:
1230:
1225:
1220:
1215:
1210:
1205:
1200:
1195:
1189:
1187:
1181:
1180:
1178:
1177:
1172:
1159:
1154:
1149:
1144:
1139:
1134:
1129:
1124:
1119:
1114:
1108:
1106:
1100:
1099:
1096:
1095:
1093:
1092:
1087:
1082:
1077:
1072:
1067:
1066:
1065:
1055:
1050:
1049:
1048:
1037:
1035:
1031:
1030:
1028:
1027:
1022:
1017:
1012:
1007:
1005:Dynamic memory
1002:
997:
992:
986:
980:
974:
973:
971:
970:
965:
960:
955:
950:
945:
940:
934:
932:
928:
927:
925:
924:
919:
914:
909:
904:
899:
894:
888:
885:
884:
877:
876:
869:
862:
854:
847:
846:External links
844:
841:
840:
820:
819:
817:
814:
811:
810:
804:
797:
793:
792:
786:
779:
775:
774:
771:
764:
760:
759:
756:
749:
745:
744:
741:
734:
726:
725:
722:
715:
707:
706:
703:
696:
688:
687:
684:
677:
669:
668:
665:
658:
650:
649:
643:
636:
628:
627:
624:
617:
609:
608:
605:
598:
590:
589:
586:
579:
571:
570:
567:
560:
552:
551:
548:
541:
533:
532:
529:
522:
514:
513:
510:
503:
495:
494:
491:
484:
476:
475:
472:
467:
436:
433:
404:
390:
380:
379:Implementation
377:
310:
288:
285:
268:
267:
265:
264:
257:
250:
242:
239:
238:
237:
236:
227:
218:
209:
197:
196:
192:
191:
190:
189:
184:
179:
174:
169:
164:
159:
154:
149:
144:
139:
131:
130:
129:General topics
126:
125:
114:
113:
28:
26:
19:
9:
6:
4:
3:
2:
1385:
1374:
1371:
1370:
1368:
1361:
1351:
1350:
1341:
1340:
1337:
1331:
1328:
1327:
1325:
1321:
1315:
1312:
1310:
1307:
1305:
1302:
1300:
1297:
1295:
1292:
1290:
1287:
1285:
1282:
1280:
1277:
1276:
1274:
1268:
1262:
1259:
1257:
1254:
1253:
1251:
1245:
1239:
1236:
1234:
1233:Visual Studio
1231:
1229:
1226:
1224:
1223:GNOME Builder
1221:
1219:
1216:
1214:
1211:
1209:
1206:
1204:
1201:
1199:
1196:
1194:
1191:
1190:
1188:
1186:
1182:
1176:
1173:
1171:
1167:
1163:
1162:Visual Studio
1160:
1158:
1155:
1153:
1150:
1148:
1145:
1143:
1140:
1138:
1135:
1133:
1130:
1128:
1125:
1123:
1120:
1118:
1115:
1113:
1110:
1109:
1107:
1105:
1101:
1091:
1088:
1086:
1083:
1081:
1078:
1076:
1073:
1071:
1068:
1064:
1061:
1060:
1059:
1056:
1054:
1051:
1047:
1044:
1043:
1042:
1039:
1038:
1036:
1032:
1026:
1023:
1021:
1018:
1016:
1013:
1011:
1008:
1006:
1003:
1001:
998:
996:
993:
991:
988:
987:
984:
981:
979:
975:
969:
966:
964:
961:
959:
956:
954:
951:
949:
946:
944:
941:
939:
936:
935:
933:
929:
923:
920:
918:
915:
913:
910:
908:
905:
903:
900:
898:
895:
893:
890:
889:
886:
882:
875:
870:
868:
863:
861:
856:
855:
852:
833:
832:
825:
821:
805:
802:
798:
794:
787:
784:
780:
776:
772:
769:
765:
761:
757:
754:
750:
746:
742:
739:
735:
732:
728:
727:
723:
720:
716:
713:
709:
708:
704:
701:
697:
694:
690:
689:
685:
682:
678:
675:
671:
670:
666:
663:
659:
656:
652:
651:
648:
644:
641:
637:
634:
630:
629:
625:
622:
618:
615:
611:
610:
606:
603:
599:
596:
592:
591:
587:
584:
580:
577:
573:
572:
568:
565:
561:
558:
554:
553:
549:
546:
542:
539:
535:
534:
530:
527:
523:
520:
516:
515:
511:
508:
504:
501:
497:
496:
492:
489:
485:
482:
478:
477:
473:
468:
463:
462:
459:
456:
454:
451:header file (
450:
446:
443:header file (
442:
432:
430:
426:
422:
418:
414:
402:
400:
388:
384:
376:
374:
308:
306:
302:
298:
294:
284:
282:
278:
274:
263:
258:
256:
251:
249:
244:
243:
241:
240:
233:
228:
224:
219:
215:
210:
206:
201:
200:
199:
198:
194:
193:
188:
185:
183:
180:
178:
175:
173:
170:
168:
165:
163:
160:
158:
155:
153:
150:
148:
145:
143:
140:
138:
135:
134:
133:
132:
128:
127:
123:
120:
119:
110:
107:
99:
88:
85:
81:
78:
74:
71:
67:
64:
60:
57: –
56:
52:
51:Find sources:
45:
41:
35:
34:
29:This article
27:
23:
18:
17:
1360:
1347:
1203:Code::Blocks
1175:Watcom C/C++
989:
963:Preprocessor
943:Header files
830:
824:
474:Description
457:
452:
448:
444:
440:
438:
428:
424:
421:isdigit(x++)
420:
412:
410:
396:
385:
382:
372:
370:
304:
290:
272:
271:
167:Localization
141:
102:
96:October 2011
93:
83:
76:
69:
62:
50:
38:Please help
33:verification
30:
1294:Objective-C
1075:Windows CRT
417:side effect
363:'z'
345:'a'
333:'Z'
315:'A'
152:Mathematics
1270:Descendant
1142:Norcroft C
968:Data types
917:Embedded C
816:References
471:character
466:character
354:&&
324:&&
137:Data types
66:newspapers
1272:languages
1104:Compilers
1046:libhybris
948:Operators
938:Functions
808:towctrans
768:towctrans
583:iswxdigit
455:in C++).
162:Date/time
1367:Category
1349:Category
1323:Designer
1238:NetBeans
1228:KDevelop
1208:CodeLite
1053:dietlibc
1020:Variadic
995:File I/O
931:Features
790:iswctype
753:iswctype
738:towupper
719:towlower
700:iswpunct
681:iswprint
662:iswblank
640:iswspace
621:iswgraph
602:iswcntrl
576:isxdigit
564:iswdigit
545:iswupper
526:iswlower
507:iswalpha
488:iswalnum
449:wctype.h
279:for the
232:stdarg.h
223:setjmp.h
205:assert.h
1213:Eclipse
1166:Express
922:MISRA C
801:wctrans
731:toupper
712:tolower
693:ispunct
674:isprint
655:isblank
633:isspace
614:isgraph
595:iscntrl
557:isdigit
538:isupper
519:islower
500:isalpha
481:isalnum
453:cwctype
441:ctype.h
429:isdigit
373:ctype.h
287:History
214:errno.h
182:Signals
147:Strings
80:scholar
1193:Anjuta
1090:uClibc
1085:Newlib
1063:EGLIBC
1041:Bionic
1010:String
958:Syntax
953:String
892:ANSI C
783:wctype
445:cctype
415:has a
124:(libc)
82:
75:
68:
61:
53:
1304:Limbo
1218:Geany
1198:CLion
1122:Clang
1070:klibc
1058:glibc
1025:POSIX
835:(PDF)
647:space
399:Linux
360:<=
348:<=
330:<=
318:<=
301:ASCII
87:JSTOR
73:books
1314:Vala
1299:Alef
1185:IDEs
1152:SDCC
1080:musl
1015:Time
1000:Math
990:Char
469:Wide
464:Byte
305:true
293:Unix
234:>
230:<
225:>
221:<
216:>
212:<
207:>
203:<
59:news
1279:C++
1170:C++
1157:TCC
1147:PCC
1137:LCC
1132:ICC
1127:GCC
1112:ACK
912:C23
907:C17
902:C11
897:C99
423:or
42:by
1369::
1309:Go
1284:C#
1168:,
1164:,
796:—
778:—
763:—
748:—
375:.
339:||
307::
1289:D
873:e
866:t
859:v
413:x
366:)
357:c
351:c
342:(
336:)
327:c
321:c
312:(
261:e
254:t
247:v
109:)
103:(
98:)
94:(
84:·
77:·
70:·
63:·
36:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
