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- Controlling expression of
if, switch(selection statement) - Controlling expression of
while,do...while(iteration statement) - S
econd operand of for(iteration statement) - First operand of
?:(selection statement) - Either operand of
|| or &&(logical operators) - Second operand of comma operator when the comma expression is used in any of these contexts
- Second and third operands of ?: (selection statement) where the ternary expression is used in any of these contexts
Noncompliant Code Example
In this noncompliant code example, an assignment expression is the outermost expression in an if statement.
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| Code Block | ||||
|---|---|---|---|---|
| ||||
do { /* ... */ } while ( foo(), (x = y) != 0) ;
|
It is less desirable in general, depending on what was intended, because it mixes the assignment in the condition, but it is clear that the programmer intended the assignment to occur.
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Exceptions
EXP18-EXP1: Assignment can be used where the result of the assignment is itself a parameter to a comparison expression or relational expression.
In this compliant example, the expression x=y is not used as the controlling expression of the while statement. is itself a parameter to a comparison operation.
| Code Block | ||||
|---|---|---|---|---|
| ||||
doif ( ( x = y ) != 0 ) { /* ... */ } while |
EXP18-EXP2: Assignment can be used where the expression consists of a single primary expression.
In this compliant example, the expression x=y is a single primary expression
| Code Block | ||||
|---|---|---|---|---|
| ||||
if ( ( x = y, ) p) =={ q ) ; |
Exceptions
/* ... */ } |
EXP18-EXP3: Assignment can be
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used in the above contexts if it occurs in a function argument or array index
In this compliant example, the expression x=y is used in a function argument
| Code Block | ||||
|---|---|---|---|---|
| ||||
if ( foo( x = y ) ) { /* ... */ } |
Noncompliant Code Example
This is a non-compliant example because && is not a comparison or relational operator and the entire expression is not primary.
| Code Block | ||||
|---|---|---|---|---|
| ||||
if ( ( v = w ) && flag ) { /* ... */ } |
Compliant Solution
When the assignment of v to w is not intended, this conditional block is now executed when v is equal to w.
| Code Block | ||||
|---|---|---|---|---|
| ||||
if ( ( |
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v == |
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w ) && flag ) { /* ... */ };
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When the assignment is intended, the following is an alternative compliant solution:
| Code Block | ||||
|---|---|---|---|---|
| ||||
if ( ( (v = w) != 0 ) && flag ) { /* ... */ } |
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; |
Risk Assessment
Errors of omission can result in unintended program flow.
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