duplicateExpressionTernary.md

duplicateExpressionTernary

Message: Same expression in both branches of ternary operator
Category: Logic
Severity: Style
Language: C/C++

Description

This checker detects when syntactically identical expressions appear in both the true and false branches of a ternary operator (condition ? true_expr : false_expr).

The warning is triggered when:

• The second and third operands of a ternary operator are syntactically identical expressions
• This includes cases where variables are referenced through aliases that resolve to the same expression

Motivation

The same expressions indicates that there might be some logic error or copy paste mistake.

Examples

Problematic code

// Same expression in both branches
int result = condition ? x : x;  // Warning: duplicateExpressionTernary

// Same variable referenced through alias
const int c = a;
int result = condition ? a : c;  // Warning: duplicateExpressionTernary

Fixed code

// Different expressions in branches
int result = condition ? x : y;  // OK

How to fix

1. Check for copy-paste errors: Verify that both branches are supposed to have the same expression
2. Use different expressions: If the branches should differ, update one of them
3. Simplify the code: If both branches are intentionally the same, remove the ternary operator entirely

Before:

int getValue(bool flag) {
    return flag ? computeValue() : computeValue();  // Same computation in both branches
}

After:

int getValue(bool flag) {
    return computeValue();  // Simplified - condition doesn't matter
}

Or if the branches should differ:

int getValue(bool flag) {
    return flag ? computeValue() : computeAlternativeValue();  // Different computations
}