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C90 defines 15 standard headers and specifies 323 names.
This is the first ISO standard for C, ratified in 1990, and is technically identical to C89.
Headers defined in C90
Names specified in C90
####define#elif#else#endif#error#if#ifdef#ifndef#include#line#pragma#undef__DATE____FILE____LINE____STDC____TIME___IOFBF_IOLBF_IONBFabortabsacosacoshasctimeasinasinhassertatanatan2atanhatexitatofatoiatolautoBUFSIZbreakbreakbreakbsearchCHAR_BIT CHAR_MAX CHAR_MIN CLOCKS_PER_ SEC calloccaseceilcharcharclearerrclockclock_tconstcontinuecoscoshctimeDBL_DECIMAL_ DIG DBL_DIG DBL_EPSILON DBL_MANT_ DIG DBL_MAX DBL_MAX_ 10_ EXP DBL_MAX_ EXP DBL_MIN DBL_MIN_ 10_ EXP DBL_MIN_ EXP DECIMAL_DIG defaultdefaultdefineddifftimedivdiv_tdodoubledoubleEDOMEOFERANGEEXIT_FAILURE EXIT_SUCCESS elseenumerrnoexitexpexternFILE *FILENAME_MAX FLT_DECIMAL_ DIG FLT_DIG FLT_EPSILON FLT_MANT_ DIG FLT_MAX FLT_MAX_ 10_ EXP FLT_MAX_ EXP FLT_MIN FLT_MIN_ 10_ EXP FLT_MIN_ EXP FLT_RADIX FLT_ROUNDS FOPEN_MAX fabsfclosefeofferrorfflushfgetcfgetposfgetsfloatfloatfloorfmodfopenforfpos_tfprintffputcfputsfreadfreefreopenfrexpfscanffseekfsetposftellfwritegetcgetchargetenvgetsgmtimegotoHUGE_VAL INT_MAX INT_MIN ifintintisalnumisalphaiscntrlisdigitisgraphislowerisprintispunctisspaceisupperisxdigitjmp_buf L_tmpnam LC_ALL LC_COLLATE LC_CTYPE LC_MONETARY LC_NUMERIC LC_TIME LDBL_DECIMAL_ DIG LDBL_DIG LDBL_EPSILON LDBL_MANT_ DIG LDBL_MAX LDBL_MAX_ 10_ EXP LDBL_MAX_ EXP LDBL_MIN LDBL_MIN_ 10_ EXP LDBL_MIN_ EXP LONG_MAX LONG_MIN labsldexplocaleconvlocaltimeloglonglonglong doublelongjmpMB_CUR_ MAX MB_LEN_ MAX mainmallocmblenmbstowcsmbtowcmemchrmemcmpmemcpymemmovememsetmktimemodfNDEBUGNULLoffsetofperrorpowprintfptrdiff_tputcputcharputsqsortRAND_MAX raiserandreallocregisterremoverenamereturnrewindSCHAR_MAX SCHAR_MIN SEEK_CUR SEEK_END SEEK_SET SHRT_MAX SHRT_MIN SIG_DFL SIG_ERR SIG_IGN SIGABRTSIGFPESIGILLSIGINTSIGSEGVSIGTERMscanfsetbufsetjmpsetlocalesetvbufshortshortsig_atomic_t signalsignedsigned charsinsinhsize_tsizeofsprintfsqrtsrandsscanfstaticstaticstaticstaticstderrstdinstdoutstrcatstrchrstrcmpstrcollstrcpystrcspnstrerrorstrftimestrlenstrncatstrncmpstrncpystrpbrkstrrchrstrspnstrstrstrtodstrtokstrtolstrtoulstructstruct lconvstruct tmstrxfrmswitchsystemTMP_MAX tantanhtimetime_ttmpfiletmpnamtolowertouppertypedefUCHAR_MAX UINT_MAX ULONG_MAX USHRT_MAX ungetcunionunsignedunsignedunsigned charunsigned longunsigned shortva_arg va_end va_list va_start vfprintfvoidvoidvoidvoidvoid *volatilevprintfvsprintfwctombwhile
