Data Directives and Operators in Inline Assembly
Although an __asm block can reference C or C++ data types and objects, it cannot define data objects with MASM directives or operators. Specifically, you cannot use the definition directives DB, DW, DD, DQ, DT, and DF, or the operators DUP or THIS. MASM structures and records are also unavailable. The inline assembler doesn't accept the directives STRUC, RECORD, WIDTH, or MASK.
END Microsoft Specific