The debugger's expression syntax is similar to that of C/C++, with a few additions and limitations. The syntax also supports Pascal-style expressions. This section discusses the following topics:

• Special Expression Features
• Expression Limitations

Expressions can refer to specific items:

• The debugger considers integer values to be 4 bytes long. Use the short data type to denote a 2-byte integer value.
• The debugger treats double values as objects 10 bytes (80 bits) in length, rather than 8 bytes (64 bits).
• To compare character strings, use the == (equal) and != (not equal) operators. The debugger distinguishes between Pascal- and C-format strings. Use the prefix \p when comparing Pascal string literals. The following expression yields a false result because it compares a C string to a Pascal string:

  "Nov shmoz ka pop" == "\pNov shmoz ka pop"
• (Mac OS) To refer to register values, use the ¨ symbol and a register name. (Type Option-r to get the ¨ symbol.)

Expressions have the following limitations:

• Do not use C/C++ preprocessor definitions and macros (defined with the #define directive). They are not available to the expression evaluator, even though the source code defines them.
• Do not use operations involving side effects. The increment (i++) and decrement (i--) operators, as well as assignments (i = j), are not allowed.
• Do not call functions.
• Do not use function names or pointers to functions.
• Do not use expression lists.
• Do not use pointers to C++ class members.
• The debugger cannot distinguish between identical variable names used in nested blocks to represent different variables (see Listing 11.4).
• Avoid using type definitions that are not available to the debugger (see Listing 11.5).
Identical Variable Names in Nested Blocks (C++):

---

// The debugger cannot distinguish between x the
// int variable and x the double variable. If x is
// used in an expression, the debugger will not
// know which one to use.

void f(void)
	{
		int x = 0;
		.
		.
		.
		{
			double x = 1.0;
			.
			.
			.
		}
	}

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Type Definitions in Expressions (C/C++):

---

// Use long in expressions; Int32 not available
typedef long Int32;

// Use Rect* in expressions; RectPtr not available
typedef Rect* RectPtr;

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• Nested type information is not available. In Listing 11.6, use Inner, not Outer::Inner in a debugger expression.
Nested Type Information (C/C++):

---

// To refer to the i member, use Inner.i,
// not Outer::Inner.i

struct Outer
	{
		struct Inner
			{
				int i;
			};
	};

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