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Using Do not use the assignment operator in the outermost expression in a conditional expression shall be diagnosed because this contexts listed in the following table because doing so typically indicates programmer error and can result in unexpected behavior.

Performing assignment statements in other contexts do not violate this rule. However, they may violate other rules, such as EXP30-C. Do not depend on the order of evaluation for side effects.

Noncompliant Code Example

In this noncompliant code example, an assignment expression is the outermost expression in a conditional expression. an if statement:

if (a = b) {
 
 /* ... */ 
} 

While this may be intendedAlthough the intent of the code may be to assign b to a and test the value of the result for equality to 0, it is almost always frequently a case of the programmer mistakenly using the assignment operator = instead of the equals operator ==. Consequently, many compilers will warn about this condition. Consequently, making this coding error would typically be eliminated by adherence detectable by adhering to MSC00-C. Compile cleanly at high warning levels.

Compliant Solution

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(Unintentional Assignment)

When the assignment of b to a is not intended, the This conditional block is now executed when a is equal to b.:

if (a == b) {
  /* ... */
}

Compliant Solution (Intentional Assignment)

When the assignment is intended, this compliant solution explicitly uses inequality as the outermost expression while performing the assignment in the inner expressionThis is an alternative compliant solution:

if ((a = b) != 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.

Noncompliant Code Example

In this noncompliant code example, the expression x = y is used as the controlling expression of the while statement:

 do { /* ... */ } while (foo(), x = y);

Compliant Solution (Unintentional Assignment)

When the assignment of y to x is not intended, the conditional block should be executed only when x is equal to y, as in this compliant solution:

do { /* ... */ } while (foo(), x == y); 

Compliant Solution (Intentional Assignment)

When the assignment is intended, this compliant solution can be used:

do { /* ... */ } while (foo(), (x = y) != 0);

Compliant Solution (for statement)

The same result can be obtained using the for statement, which is specifically designed to evaluate an expression on each iteration of the loop, just before performing the test in its controlling expression. Remember that its controlling expression is the second operand, where the assignment occurs in its third operand:

 for (; x; foo(), x = y) { /* ... */ }

Noncompliant Code Example

In this noncompliant example, the expression p = q is used as the controlling expression of the while statement:

 do { /* ... */ } while (x = y, p = q);

Compliant Solution

In this compliant solution, the expression x = y is not used as the controlling expression of the while statement:

do { /* ... */ } while (x = y, p == q); 

Noncompliant Code Example

while (ch = '\t' || ch == ' ' || ch == '\n') {
  /* ... */
}

while ('\t' = ch || ' ' == ch || '\n' == ch) {
  /* ... */
}

while ('\t' == ch || ' ' == ch || '\n' == ch) {
  /* ... */
}

if ((x = y) != 0) { /* ... */ } 

if ((x = y)) { /* ... */ } 

if ((v = w) && flag) { /* ... */ } 

if ((v == w) && flag) { /* ... */ }; 

if (((v = w) != 0) && flag) { /* ... */ }; 

if (foo(x = y)) { /* ... */ } 

Errors of omission can result in unintended program flow.

Automated Detection

The LDRA tool suite Version 7.6.0 can detect violations of this recommendation???

GCC Compiler Version 4.4.0 can detect violations of this recommendation when the -Wall flag is used???

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Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Other Languages

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Related Guidelines

Key here (explains table format and definitions)

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CERT-CWE Mapping Notes

Key here for mapping notes

CWE-480 and EXP45-C

Intersection( EXP45-C, EXP46-C) = Ø

CWE-480 = Union( EXP45-C, list) where list =

• Usage of incorrect operator besides s/=/==/

CWE-569 and EXP45-C

CWE-480 = Subset( CWE-569)

Bibliography

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Bibliography

Wiki Markup\[[Hatton 95|AA. References#Hatton 95]\] Section 2.7.2, "Errors of omission and addition" \[[ISO/IEC PDTR 24772|AA. References#ISO/IEC PDTR 24772]\] "KOA Likely Incorrect Expressions" \[[MITRE 07|AA. References#MITRE 07]\] [CWE ID 480|http://cwe.mitre.org/data/definitions/480.html], "Use of Incorrect Operator"