The C Run-Time Library (CRT) supports American National Standards Institute (ANSI) C and UNIX C. When this documentation references UNIX, it includes XENIX, other UNIX-like systems, and the POSIX subsystem in Windows 2000, Windows XP, Windows Server 2003, Windows Vista, Windows 7, and Windows 8.

All CRT routines that are included in the following products are compatible with the Windows API.

  • ANSI

  • ISO C 95

  • Windows 2000

  • Windows XP

  • Windows Server 2003

  • Windows Vista

  • Windows 7

The CRT routines in Windows 8 are compatible with the Windows API, except that some of the routines, which are listed in CRT functions not supported with /ZW, are not supported by the Windows Runtime.



Windows Store Apps, the Windows Runtime, and the C Run-Time

Describes when CRT routines are not compatible with Windows Store apps.

ANSI C Compliance

Describes ANSI-compliant naming in the CRT.


Provides guidelines for porting programs to UNIX.

Windows Platforms (CRT)

Lists the operating systems that are the CRT supports.

Backward Compatibility

Describes how to map old CRT names to the new ones.

CRT Library Features

Provides an overview of the CRT library (.lib) files and the associated compiler options.