Do not use the assignment operator in the outermost expression of an if or switch statement or a looping statement (while, do, or for) because this typically indicates programmer error and can result in unexpected behavior.
Noncompliant Code Example
In this noncompliant code example, an assignment expression is the outermost expression in an if statement.
if (a = b) {
/* ... */
}
While the intent of the code may be to assign b to a and test the value of the result for equality to zero, it is very frequently a case of the programmer mistakenly using the assignment operator = instead of the equals operator ==.
Compliant Solution
When the assignment of b to a is not intended, this conditional block is now executed when a is equal to b.
if (a == b) {
/* ... */
}
When the assignment is, if fact, intended, this is an alternative compliant solution:
if ((a = b) == true) {
/* ... */
}
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.
Risk Assessment
Errors of omission can result in unintended program flow.
Recommendation |
Severity |
Likelihood |
Remediation Cost |
Priority |
Level |
|---|---|---|---|---|---|
EXP04-J |
low |
likely |
medium |
P6 |
L2 |
Related Guidelines
CERT C++ Secure Coding Standard: EXP19-CPP. Do not perform assignments in conditional expressions
CERT C Secure Coding Standard: EXP18-C. Do not perform assignments in selection statements
ISO/IEC TR 24772 "KOA Likely Incorrect Expressions"
MITRE CWE: CWE-480, "Use of Incorrect Operator"
Bibliography
[[Hatton 1995]] Section 2.7.2, "Errors of omission and addition"
EXP17-C. Do not perform bitwise operations in conditional expressions 03. Expressions (EXP) EXP19-C. Use braces for the body of an if, for, or while statement