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The Microsoft C compiler supports the ANSI C standard. In addition, it offers a number of features beyond those specified in the ANSI C standard. These features are available when the /Ze option, the default, is specified and are not available when the /Za option is specified. See Microsoft Extensions to C for more information.
| Command Line | Project Settings | Description |
| /Za | Disable Language Extensions (check box selected) | ANSI C compatibility. Language constructs not compatible with ANSI C are flagged as errors. |
| /Ze | (Check box cleared) | Enables Microsoft extensions. |
To find this option in the development environment, click Settings on the Project menu. Then click the C/C++ tab, and click Customize in the Category box.
Note If you use the Disable Language Extensions (/Za) option, the Improve Float Consistency (/Op) option is used to improve the consistency of floating-point tests for equality and inequality. This use of /Op with /Za is for strict ANSI conformance and is the only situation under which /Op is selected by default. The /Op– option is provided to override the default selection of /Op with /Za. Specify /Op– in the Common/Project/Source File Options text box (or on the command line), after /Za, to disable /Op. For more information, also see Generate Intrinsic Functions (/Oi).
Disable language extensions if you plan to port your program to other environments. The compiler treats extended keywords as simple identifiers, disables the other Microsoft extensions, and automatically defines the __STDC__ predefined macro for C programs.