bugprone-redundant-branch-condition¶
Finds condition variables in nested if
statements that were also checked in
the outer if
statement and were not changed.
Simple example:
bool onFire = isBurning();
if (onFire) {
if (onFire)
scream();
}
Here onFire is checked both in the outer if
and the inner if
statement
without a possible change between the two checks. The check warns for this code
and suggests removal of the second checking of variable onFire.
The checker also detects redundant condition checks if the condition variable
is an operand of a logical “and” (&&
) or a logical “or” (||
) operator:
bool onFire = isBurning();
if (onFire) {
if (onFire && peopleInTheBuilding > 0)
scream();
}
bool onFire = isBurning();
if (onFire) {
if (onFire || isCollapsing())
scream();
}
In the first case (logical “and”) the suggested fix is to remove the redundant
condition variable and keep the other side of the &&
. In the second case
(logical “or”) the whole if
is removed similarly to the simple case on the
top.
The condition of the outer if
statement may also be a logical “and” (&&
)
expression:
bool onFire = isBurning();
if (onFire && fireFighters < 10) {
if (someOtherCondition()) {
if (onFire)
scream();
}
}
The error is also detected if both the outer statement is a logical “and”
(&&
) and the inner statement is a logical “and” (&&
) or “or” (||
).
The inner if
statement does not have to be a direct descendant of the outer
one.
No error is detected if the condition variable may have been changed between the two checks:
bool onFire = isBurning();
if (onFire) {
tryToExtinguish(onFire);
if (onFire && peopleInTheBuilding > 0)
scream();
}
Every possible change is considered, thus if the condition variable is not a local variable of the function, it is a volatile or it has an alias (pointer or reference) then no warning is issued.
Known limitations¶
The else
branch is not checked currently for negated condition variable:
bool onFire = isBurning();
if (onFire) {
scream();
} else {
if (!onFire) {
continueWork();
}
}
The checker currently only detects redundant checking of single condition variables. More complex expressions are not checked:
if (peopleInTheBuilding == 1) {
if (peopleInTheBuilding == 1) {
doSomething();
}
}