V721. The VARIANT_BOOL type is utilized incorrectly. The true value (VARIANT_TRUE) is defined as -1.

The analyzer has detected an incorrect use of the VARIANT_BOOL type. The reason is that the value true (VARIANT_TRUE) is designated as -1. Many programmers are unaware of this detail and tend to use this type incorrectly.

This is how the VARIANT_TRUE type and constants denoting "true" and "false" are declared:

typedef short VARIANT_BOOL;

Let's take a look at a few examples when the VARIANT_TRUE type is used incorrectly. In all the cases, the programmer expects the condition to be true, while it is actually always false.

Example 1.

if (variantBoolTrue == true) //false 

If we substitute the value into the expression, we'll get ((short)(-1) == true). When this expression is evaluated, 'true' will turn into '1'. The condition (-1 == 1) is false.

The correct code:

if (variantBoolTrue == VARIANT_TRUE)

Example 2.

VARIANT_BOOL variantBoolTrue = TRUE;
if (variantBoolTrue == VARIANT_TRUE) //false

The programmer made a mistake here and used TRUE instead of VARIANT_TRUE. It will result in the variantBoolTrue variable being assigned the value 1. This value is illegal for variables of the VARIANT_BOOL type.

If we substitute the value into the expression, we will get (1 == (short)(-1)).

The correct code:


Example 3.

bool bTrue = true;
if (bTrue == VARIANT_TRUE) //false

Let's expand the expression: (true == (short)(-1)). When it is evaluated, 'true' will turn into '1'. The condition (1 == -1) is false.

It's not easy to suggest a correct version of this code as it is just fundamentally incorrect. One can't mix variables of the 'bool' type and values of the 'VARIANT_TRUE' type.

There are numbers of other examples like these to be found in code. For instance, when a function's formal argument is of the VARIANT_BOOL type but it is the 'true' value that will be passed as the actual one. Another example is when a function returns an incorrect value. And so on and so forth.

The most important thing you should keep in mind is that you can't mix the VARIANT_BOOL type with the types BOOL, bool, and BOOLEAN.


According to Common Weakness Enumeration, potential errors found by using this diagnostic are classified as CWE-665, CWE-697.

You can look at examples of errors detected by the V721 diagnostic.

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