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These options undefine previously defined symbols.
| Command Line | Project Settings | Description |
| /Usymbol | Undefined Symbols | Undefines a previously defined symbol |
| /u | Undefine All Symbols | Turns off every previously defined symbol |
Type the name of a previously defined macro in the text box to undefine it. (Or specify symbol on the command line. A space between /U and symbol is optional.) To undefine additional macros, type additional ones, using a space to separate each. (On the command line, simply repeat /Usymbol.)
To find these options in the development environment, click Settings on the Project menu. Then click the C/C++ tab, and click Preprocessor in the Category box.
Neither of these options can be used to undefine symbols created with the #define directive. Both options turn off the following Microsoft-specific macros:
| Symbol | Function |
| _CHAR_UNSIGNED | Default char type is unsigned. Defined when /J is specified. |
| _CPPRTTI | Defined for code compiled with the /GR (Enable Run-Time Type Information) option. |
| _CPPUNWIND | Defined for code compiled with the /GX (Enable Exception Handling) option. |
| _DLL | Defined when /MD is specified. |
| _M_IX86 | 1Defined as 500 for Blend (/GB), 300 for 80386 (/G3), 400 for 80486 (/G4), 500 for Pentium (/G5), and 600 for Pentium Pro (/G6). |
| _MSC_VER | Defines the compiler version. Defined as 1200 for Microsoft Visual C++ version 6.0. Always defined. |
| _WIN32 | 2Defined for applications for WIN32. Always defined. |
| _MT | Defined when /MD or /MT is specified. |
1 x86 specific
2 x86 specific