/fullpaths (Specify Fully Qualified Path in Compiler Output) (C# Compiler Options)
The /fullpaths option causes the compiler to specify the full path to the file when listing compilation errors and warnings.
/fullpaths
Remarks
By default, errors and warnings that result from compilation specify the name of the file in which an error was found. The /fullpaths option causes the compiler to specify the full path to the file.
This compiler option is unavailable in Visual Studio and cannot be changed programmatically.