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Useless if

Unnecessary if conditional

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Description

This defect occurs on if-statements where the condition is always true. This defect occurs only on if-statements that do not have an else-statement.

This defect shows unnecessary if-statements when there is no difference in code execution if the if-statement is removed.

Risk

Unnecessary if statements often indicate a coding error. Perhaps the if condition is coded incorrectly or the if statement is not required at all.

Fix

The fix depends on the root cause of the defect. For instance, the root cause can be an error condition that is checked twice on the same execution path, making the second check redundant.

Often the result details (or source code tooltips in Polyspace as You Code) show a sequence of events that led to the defect. You can implement the fix on any event in the sequence. If the result details do not show this event history, you can search for previous references of variables relevant to the defect using right-click options in the source code and find related events. See also Interpret Bug Finder Results in Polyspace Desktop User Interface or Interpret Bug Finder Results in Polyspace Access Web Interface (Polyspace Access).

See examples of fixes below.

If the redundant condition represents defensive coding practices and you do not want to fix the issue, add comments to your result or code to avoid another review. See:

Examples

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typedef enum _suit {UNKNOWN_SUIT, SPADES, HEARTS, DIAMONDS, CLUBS} suit;
suit nextcard(void);
void do_something(suit s);

void bridge(void)
{
    suit card = nextcard();
    if ((card < SPADES) || (card > CLUBS)){
        card = UNKNOWN_SUIT;
    }

    if (card < 7) {
        do_something(card);
    }
}

The type suit is enumerated with five options. However, the conditional expression card < 7 always evaluates to true because card can be at most 5. The if statement is unnecessary.

Correction — Change Condition

One possible correction is to change the if-condition in the code. In this correction, the 7 is changed to UNKNOWN_SUIT to relate directly to the type of card.

typedef enum _suit {UNKNOWN_SUIT, SPADES, HEARTS, DIAMONDS, CLUBS} suit;
suit nextcard(void);
void do_something(suit s);

void bridge(void)
{
    suit card = nextcard();
    if ((card < SPADES) || (card > CLUBS)){
        card = UNKNOWN_SUIT;
    }

    if (card > UNKNOWN_SUIT) {
        do_something(card);
    }
}
Correction — Remove If

Another possible correction is to remove the if-condition in the code. Because the condition is always true, you can remove the condition to simplify your code.

typedef enum _suit {UNKNOWN_SUIT, SPADES, HEARTS, DIAMONDS, CLUBS} suit;
suit nextcard(void);
void do_something(suit s);

void bridge(void)
{
    suit card = nextcard();
    if ((card < SPADES) || (card > CLUBS)){
        card = UNKNOWN_SUIT;
    }

    do_something(card);
}

Result Information

Group: Data flow
Language: C | C++
Default: On
Command-Line Syntax: USELESS_IF
Impact: Medium

Version History

Introduced in R2013b

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See Also

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