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In this noncompliant code example, i is evaluated more than one in an unsequenced manner, and so the behavior of the expression is undefined:

Code Block

bgColor	#FFcccc
lang	cpp

void f(int i, const int *b) {
  int a = i + b[++i];
  // ...
}

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The call to func() in this noncompliant code example has undefined behavior because the argument expressions are unsequenced:

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The order of evaluation for function arguments is unspecified. This noncompliant code example exhibits unspecified behavior but not undefined behavior:

Code Block

bgColor	#FFcccc
lang	c

extern void c(int i, int j);
int glob;
 
int a() {
  return glob + 10;
}

int b() {
  glob = 42;
  return glob;
}
 
void f() {
  c(a(), b());
}

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Attempting to modify an object in an unsequenced or indeterminately sequenced evaluation may cause that object to take on an unexpected value, which can lead to unexpected program behavior.

Rule	Severity	Likelihood	Remediation Cost	Priority	Level
EXP30EXP50-CPP	Medium	Probable	Medium	P8	L2

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Tool

Version

Checker

Description

Compass/ROSE

Can detect simple violations of this rule. It needs to examine each expression and make sure that no variable is modified twice in the expression. It also must check that no variable is modified once, then read elsewhere, with the single exception that a variable may appear on both the left and right of an assignment operator

Coverity

Include Page

	Coverity_V
	Coverity_V

EVALUATION_ORDER

Can detect the specific instance where a statement contains multiple side effects on the same value with an undefined evaluation order because, with different compiler flags or different compilers or platforms, the statement may behave differently

ECLAIR

Include Page

	ECLAIR_V
	ECLAIR_V

CC2.EXP30

Fully implemented

GCC

Include Page

	GCC_V
	GCC_V

Can detect violations of this rule when the -Wsequence-point flag is used

LDRA tool suite

Include Page

	LDRA_V
	LDRA_V

35 D
1 Q
9 S
134 S

Fully implemented

Splint

Include Page

	Splint_V
	Splint_V

PRQA QA-C++

Include Page

	PRQA QA-C++_V
	PRQA QA-C++_V

3220, 3221, 3222, 3223

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CERT C Secure Coding Standard

EXP30-C. Do not depend on the order of evaluation for side effects

Bibliography

[ISO/IEC 14882-2014]	1.9, "Program Execution"
[MISRA 08]	Rule 5-0-1, "The value of an expression shall be the same under any order of evaluation that the standard permits."

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Old Version 34

New Version 35

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Bibliography