duplicateValueTernary

Message: Same value in both branches of ternary operator

Category: Logic

Severity: Style

Language: C/C++

Description

This checker detects when both branches of a ternary operator (condition ? true_expr : false_expr) evaluate to the same value, even though the expressions themselves may be syntactically different.

The warning is triggered when:

• The second and third operands of a ternary operator evaluate to the same constant value
• The expressions are constant statements that don't change during evaluation
• The expressions have different syntax but equivalent values

However, no warning is generated when:

• The expressions have different values on different platforms
• Variables are modified between evaluations
• The expressions involve non-constant computations

Motivation

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

Examples

Problematic code

// Different expressions, same value
int result = condition ? (int)1 : 1;  // Warning: duplicateValueTernary

// Different cast syntax, same value
int result = condition ? 1 : (int)1;  // Warning: duplicateValueTernary

Fixed code

// Different values in branches
int result = condition ? 1 : 2;  // OK

// Simplified - condition doesn't matter
int result = 1;  // OK - removed unnecessary ternary

// Platform-dependent values are allowed
int size = is_64bit ? sizeof(long) : sizeof(int);  // OK - may differ on platforms

How to fix

1. Check for logic errors: Verify if both branches should actually have the same value
2. Simplify the code: If both branches always have the same value, remove the ternary operator
3. Use different values: If the branches should differ, update one of them
4. Remove unnecessary casts: If the difference is only in casting, consider if the cast is needed

Before:

int getValue(bool flag) {
    return flag ? (int)42 : 42;  // Same value, different expressions
}

After (simplified):

int getValue(bool flag) {
    return 42;  // Simplified - condition doesn't affect result
}

Or (if branches should differ):

int getValue(bool flag) {
    return flag ? 42 : 0;  // Different values for different conditions
}