Each assembly-language statement can contain only one C or C++ symbol. Multiple symbols can appear in the same assembly instruction only with LENGTH, TYPE, and SIZE expressions. You can also use two symbols if one is a register variable.An __asm block can refer to any C or C++ symbol in scope where the block appears. (C and C++ symbols are variable names, function names, and labels; that is, names that aren't symbolic constants or enum members. You cannot call C++ member functions.)
A few restrictions apply to the use of C and C++ symbols:
Each assembly-language statement can contain only one C or C++ symbol. Multiple symbols can appear in the same assembly instruction only with LENGTH, TYPE, and SIZE expressions. You can also use two symbols if one is a register variable.
Functions referenced in an __asm block must be declared (prototyped) earlier in the program. Otherwise, the compiler cannot distinguish between function names and labels in the __asm block.
An __asm block cannot use any C or C++ symbols with the same spelling as MASM reserved words (regardless of case). MASM reserved words include instruction names such as PUSH and register names such as SI.
Structure and union tags are not recognized in __asm blocks.