/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.
/J
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.
Note
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.
Open your project's Property Pages dialog box. For details, see Set C++ compiler and build properties in Visual Studio.
Select the Configuration Properties > C/C++ > Command Line property page.
In Additional Options, enter the /J compiler option.
MSVC Compiler Options
MSVC Compiler Command-Line Syntax
Set C++ compiler and build properties in Visual Studio