/J (Default char Type Is unsigned)
Changes the default char type from signed char to unsigned char, and the char type is zero-extended when it is widened to an int type.
If a char value is explicitly declared as signed, the /J option does not affect it, and the value is sign-extended when it is widened to an int type.
The /J option defines _CHAR_UNSIGNED, which is used with #ifndef in the LIMITS.h file to define the range of the default char type.
ANSI C and C++ do not require a specific implementation of the char type. This option is useful when you are working with character data that will eventually be translated into a language other than English.
If you use this compiler option with ATL/MFC, an error might be generated. Although you could disable this error by defining _ATL_ALLOW_CHAR_UNSIGNED, this workaround is not supported and may not always work.
To set this compiler option in the Visual Studio development environment
In Solution Explorer, open the shortcut menu for the project and then choose Properties.
In the project Property Pages dialog box, in the left pane under Configuration Properties, expand C/C++ and then select Command Line.
In the Additional Options pane, specify the /J compiler option.