Invalid Boolean value

Overview

Use this check to detect accesses to a Boolean variable when its value isn’t true or false. This problem can occur when using an integer or pointer without an appropriate cast. The use of out-of-range Boolean values has undefined behavior, which can be difficult to debug. Available in Xcode 9 and later.

Invalid Boolean variable access in C

The intent of the following code is to call the success function when result is nonzero. However, because it uses a Boolean check, the compiler may, as an optimization, only emit instructions that check the least-significant bit of predicate, which is 0, causing a logic error.

int result = 2;
bool *predicate = (bool *)&result;
if (*predicate) { // Error: variable is not a valid Boolean
    success();
}

Solution

Use integer comparison instead of a Boolean check.

int result = 2;
if (result != 0) { // Correct
  success();
}

See Also

Undefined Behavior Sanitizer

• Misaligned pointer
• Out-of-bounds array access
• Invalid enumeration value
• Reaching of unreachable point
• Dynamic type violation
• Invalid float cast
• Division by zero
• Nonnull argument violation
• Nonnull return value violation
• Nonnull variable assignment violation
• Null reference creation and null pointer dereference
• Invalid object size
• Invalid shift
• Integer overflow
• Invalid variable-length array