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CRT functions not supported in Universal Windows Platform apps

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Many C runtime (CRT) functions aren't available when you build Universal Windows Platform (UWP) apps. Sometimes workarounds are available—-for example, you can use Windows Runtime or Win32 APIs. In other cases, CRT functions have been banned because the corresponding features or the supporting APIs aren't applicable to UWP apps. To look for an alternative method that's supported for the Windows Runtime, see Alternatives to Windows APIs in UWP apps.

The following table lists the CRT functions that are unavailable when you build UWP apps. It indicates any workarounds that apply.

Unsupported CRT Functions

Function Description Workaround
_beep _sleep _seterrormode These functions were obsolete in previous versions of the CRT. Also, the corresponding Win32 APIs are not available for UWP apps. No workaround.
chdir _chdrive getcwd These functions are obsolete or are not thread-safe. Use _chdir, _getcwd and related functions.
_cgets _cgets_s _cgetws _cgetws_s _cprintf _cprintf_l _cprintf_p _cprintf_p_l _cprintf_s _cprintf_s_l _cputs _cputws _cscanf _cscanf_l _cscanf_s _cscanf_s_l _cwait _cwprintf _cwprintf_l _cwprintf_p _cwprintf_p_l _cwprintf_s _cwprintf_s_l _cwscanf _cwscanf_l _cwscanf_s _cwscanf_s_l _vcprintf _vcprintf_l _vcprintf_p _vcprintf_p_l _vcprintf_s _vcprintf_s_l _vcwprintf _vcwprintf_l _vcwprintf_p _vcwprintf_p_l _vcwprintf_s _vcwprintf_s_l _getch _getch_nolock _getche _getche_nolock _getwch _getwch_nolock _getwche _getwche_nolock _putch _putch_nolock _putwch _putwch_nolock _ungetch _ungetch_nolock _ungetwch _ungetwch_nolock _kbhit kbhit putch cgets cprintf cputs cscanf cwait getch getche ungetch These console I/O functions are unavailable in GUI-based UWP apps. UWP console apps can use these functions. For more information, see Create a Universal Windows Platform console app.
getpid _getpid These functions are obsolete. Use the Win32 API GetCurrentProcessId.
_getdiskfree Not available. Use the Win32 API GetDiskFreeSpaceExW.
_getdrive _getdrives Corresponding API is not available for UWP apps. No workaround.
_inp _inpd _inpw _outp _outpd _outpw inp inpd inpw outp outpd outpw Port IO is not supported in UWP apps. No workaround.
_ismbcalnum _ismbcalnum_l _ismbcalpha _ismbcalpha_l _ismbcdigit _ismbcdigit_l _ismbcgraph _ismbcgraph_l _ismbchira _ismbchira_l _ismbckata _ismbckata_l _ismbcl0 _ismbcl0_l _ismbcl1 _ismbcl1_l _ismbcl2 _ismbcl2_l _ismbclegal _ismbclegal_l _ismbclower _ismbclower_l _ismbcprint _ismbcprint_l _ismbcpunct _ismbcpunct_l _ismbcspace _ismbcspace_l _ismbcsymbol _ismbcsymbol_l _ismbcupper _ismbcupper_l _mbbtombc _mbbtombc_l _mbbtype _mbbtype_l _mbccpy _mbccpy_l _mbccpy_s _mbccpy_s_l _mbcjistojms _mbcjistojms_l _mbcjmstojis _mbcjmstojis_l _mbclen _mbclen_l _mbctohira _mbctohira_l _mbctokata _mbctokata_l _mbctolower _mbctolower_l _mbctombb _mbctombb_l _mbctoupper _mbctoupper_l _mbsbtype _mbsbtype_l _mbscat _mbscat_l _mbscat_s _mbscat_s_l _mbschr _mbschr_l _mbscmp _mbscmp_l _mbscoll _mbscoll_l _mbscpy _mbscpy_l _mbscpy_s _mbscpy_s_l _mbscspn _mbscspn_l _mbsdec _mbsdec_l _mbsicmp _mbsicmp_l _mbsicoll _mbsicoll_l _mbsinc _mbsinc_l _mbslen _mbslen_l _mbslwr _mbslwr_l _mbslwr_s _mbslwr_s_l _mbsnbcat _mbsnbcat_l _mbsnbcat_s _mbsnbcat_s_l _mbsnbcmp _mbsnbcmp_l _mbsnbcnt _mbsnbcnt_l _mbsnbcoll _mbsnbcoll_l _mbsnbcpy _mbsnbcpy_l _mbsnbcpy_s _mbsnbcpy_s_l _mbsnbicmp _mbsnbicmp_l _mbsnbicoll _mbsnbicoll_l _mbsnbset _mbsnbset_l _mbsnbset_s _mbsnbset_s_l _mbsncat _mbsncat_l _mbsncat_s _mbsncat_s_l _mbsnccnt _mbsnccnt_l _mbsncmp _mbsncmp_l _mbsncoll _mbsncoll_l _mbsncpy _mbsncpy_l _mbsncpy_s _mbsncpy_s_l _mbsnextc _mbsnextc_l _mbsnicmp _mbsnicmp_l _mbsnicoll _mbsnicoll_l _mbsninc _mbsninc_l _mbsnlen _mbsnlen_l _mbsnset _mbsnset_l _mbsnset_s _mbsnset_s_l _mbspbrk _mbspbrk_l _mbsrchr _mbsrchr_l _mbsrev _mbsrev_l _mbsset _mbsset_l _mbsset_s _mbsset_s_l _mbsspn _mbsspn_l _mbsspnp _mbsspnp_l _mbsstr _mbsstr_l _mbstok _mbstok_l _mbstok_s _mbstok_s_l _mbsupr _mbsupr_l _mbsupr_s _mbsupr_s_l is_wctype Multi-byte strings are not supported in UWP apps. Use Unicode strings instead.
_pclose _pipe _popen _wpopen Pipe functionality is not available to UWP apps. No workaround.
_resetstkoflw Supporting Win32 APIs are not available for UWP apps. No workaround.
_getsystime _setsystime These were obsolete APIs in previous CRT versions. Also, a user cannot set the system time in a UWP app due to lack of permissions. To get the system time only, use the Win32 API GetSystemTime. System time cannot be set.
_environ _putenv _putenv_s _searchenv _searchenv_s _dupenv_s _wputenv _wputenv_s _wsearchenv getenv getenv_s putenv _wdupenv_s _wenviron _wgetenv _wgetenv_s _wsearchenv_s tzset Environment variables are not available to UWP apps. No workaround. To set the time zone, use _tzset.
_loaddll _getdllprocaddr _unloaddll These were obsolete functions in previous CRT versions. Also, a user can't load DLLs except the ones in the same application package. Use Win32 APIs LoadPackagedLibrary, GetProcAddress, and FreeLibrary to load and use packaged DLLs.
_wexecl _wexecle _wexeclp _wexeclpe _wexecv _wexecve _wexecvp _wexecvpe _execl _execle _execlp _execlpe _execv _execve _execvp _execvpe _spawnl _spawnle _spawnlp _spawnlpe _spawnv _spawnve _spawnvp _spawnvpe _wspawnl _wspawnle _wspawnlp _wspawnlpe _wspawnv _wspawnve _wspawnvp _wspawnvpe _wsystem execl execle execlp execlpe execv execve execvp execvpe spawnl spawnle spawnlp spawnlpe spawnv spawnve spawnvp spawnvpe system The functionality is not available in UWP apps. A UWP app cannot invoke another UWP app or a desktop app. No workaround.
_heapwalk _heapadd _heapchk _heapset _heapused These functions are typically used to work with the heap. However, corresponding Win32 APIs are not supported in UWP apps. And, apps can no longer create or use private heaps. No workaround. However, _heapwalk is available in the DEBUG CRT, for debugging purposes only. These functions can't be used in apps that are uploaded to the Microsoft Store.

The following functions are available in the CRT for UWP apps. However, use them only when you can't use the corresponding Win32 or Windows Runtime APIs, such as when you're porting large code bases:

Functions Workaround
Single-byte string functions—for example, strcat, strcpy, strlwr, and so on. Make your UWP apps strictly Unicode because all Win32 APIs and Windows Runtime APIs that are exposed use Unicode character sets only. Single-byte functions were left for porting large code bases, but should otherwise be avoided. The corresponding wide char functions should be used instead when possible.
Stream IO and low-level file IO functions—for example, fopen, open, and so on. These functions are synchronous, which isn't recommended for UWP apps. In your UWP apps, use asynchronous APIs to open, read from, and write to files to prevent locking of the UI thread. Examples of such APIs are the ones in the Windows::Storage::FileIO class.

Windows 8.x Store apps and Windows Phone 8.x apps

Both the previously mentioned APIs and the following APIs are unavailable in Windows 8.x Store apps and Windows Phone 8.x apps.

Functions Description Workaround
_beginthread _beginthreadex _endthread _endthreadex Threading Win32 APIs are not available in Windows 8.x Store apps. Use the Windows Runtime Windows::System::Threading::ThreadPool or concurrency::task instead.
_chdir _wchdir _getcwd _getdcwd _wgetcwd _wgetdcwd The concept of a working directory doesn't apply to Windows 8.x Store apps. Use full paths instead.
_isleadbyte_l _ismbbalnum, _ismbbalnum_l, _ismbbalpha, _ismbbalpha _ismbbalpha_l _ismbbgraph _ismbbgraph_l _ismbbkalnum _ismbbkalnum_l _ismbbkana _ismbbkana_l _ismbbkprint _ismbbkprint_l _ismbbkpunct _ismbbkpunct_l _ismbblead _ismbblead_l _ismbbprint _ismbbprint_l _ismbbpunct _ismbbpunct_l _ismbbtrail _ismbbtrail_l _ismbslead _ismbslead_l _ismbstrail _ismbstrail_l _mbsdup isleadbyte Multi-byte strings are not supported in Windows 8.x Store apps. Use Unicode strings instead.
_tzset Environment variables are not available to Windows 8.x Store apps. No workaround.
_get_heap_handle, _heapmin The corresponding Win32 APIs are not supported in Windows 8.x Store apps. And, apps can no longer create private heaps. No workaround. However, _get_heap_handle is available in the DEBUG CRT, for debugging purposes only.