Using C or C++ Symbols in __asm Blocks

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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.

  • 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.