National Instruments 320685D-01 Details of User Protection Pointer Casting

Chapter 1 LabWindows/CVI Compiler

LabWindows/CVI Programmer Reference Manual 1-14

National Instruments Corporation

These two pragmas enable and disable run-time checking for a particular library function

throughout the module in which they appear. You can use them to override the effects of the

EnableLibraryRuntimeChecking and DisableLibraryRuntimeChecking pragmas

for individual functions. If both of these pragmas occur in a module for the same function,

LabWindows/CVI uses only the last occurrence.

Note These pragmas affect all protection, including run-time checking of function

arguments, for all calls to a specific library function. To disable breaking on

errors for a particular call to a library function, use the Utility Library function

SetBreakOnLibraryErrors. To disable the run-time checking of argument

expressions for a particular call to a library function, use the Utility Library

function SetBreakOnProtectionErrors.

Note You cannot use pragmas to disable protection for the functions in the

statically linked libraries including User Interface, RS-232, TCP, DDE,

Formatting and I/O, Utility, X Property, and ANSI C libraries unless you place the

DisableLibraryRuntimeChecking pragma at the top of the library header file.

Details of User ProtectionPointer Casting

A cast expression consists of a left parenthesis, a type name, a right parenthesis, and an

operand expression. The cast causes the compiler to convert the operand value to the type that

appears within the parenthesis.

C programmers occasionally have to cast a pointer to one data type to a pointer to another data

type. Because LabWindows/CVI does not restructure the user protection information for each

cast expression, certain types of cast expressions implicitly disable run-time checking for the

pointer value. In particular, casting a pointer expression to the following types disables

run-time checking on the resulting value:

• Pointer to a pointer: (AnyType **) PointerExpression

• Pointer to a structure:(struct AnyStruct *) PointerExpression

• Pointer to an array:(AnyType (*)[]) PointerExpression

• Any non-pointer type:(unsigned) PointerExpression,

(int) PointerExpression, and so on

Note An exception exists. Casts that you apply implicitly or explicitly to the void *

values you obtain from malloc or calloc do not disable user protection.

Casting a pointer to one arithmetic type to a pointer to a different one, such as (int *),

(unsigned *), (short *), and so on, does not affect run-time checking on the resulting

pointer, nor does casting a pointer to a void pointer (void *).