/Za, /Ze (Disable Language Extensions)
The /Za compiler option disables and emits errors for Microsoft extensions to C that aren't compatible with ANSI C89/ISO C90. The deprecated /Ze compiler option enables Microsoft extensions. Microsoft extensions are enabled by default.
The use of /Za when code is compiled as C++ is not recommended. The /Ze option is deprecated because its behavior is on by default. For a list of deprecated compiler options, see Deprecated and removed compiler options.
The Microsoft C/C++ compiler supports compilation of C code in two ways:
The compiler uses C compilation mode by default when a source file has a .c extension, or when the /Tc or /TC option is specified. The C compiler is an C89/C90 compiler that, by default, enables Microsoft extensions to the C language. For more information about specific extensions, see Microsoft Extensions to C and C++. When both C compilation and the /Za option are specified, the C compiler conforms strictly to the C89/C90 standard. The compiler treats Microsoft extended keywords as simple identifiers, disables the other Microsoft extensions, and automatically defines the __STDC__ predefined macro for C programs.
The compiler can compile C code in C++ compilation mode. This behavior is the default for source files that don't have a .c extension, and when the /Tp or /TP option is specified. In C++ compilation mode, the compiler supports those parts of the ISO C99 and C11 standards that have been incorporated into the C++ standard. Almost all C code is also valid C++ code. A small number of C keywords and code constructs aren't valid C++ code, or are interpreted differently in C++. The compiler behaves according to the C++ standard in these cases. In C++ compilation mode, the /Za option may cause unexpected behavior and isn't recommended.
Other compiler options can affect how the compiler ensures standards conformance. For ways to specify specific standard C and C++ behavior settings, see the /Zc compiler option. For additional C++ standard conformance settings, see the /permissive- and /std compiler options.
For more information about conformance issues with Visual C++, see Nonstandard Behavior.
To set this compiler option in the Visual Studio development environment
Open the project's Property Pages dialog box. For details, see Set C++ compiler and build properties in Visual Studio.
Select the Configuration Properties > C/C++ > Language property page.
Modify the Disable Language Extensions property.