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Code Block

bgColor	#FFCCCC
lang	c

int func(int condition) {
    char *s = NULL;
    if (condition) {
        s = (char *)malloc(10);
        if (s == NULL) {
           /* Handle Error */
        }
        /* Process s */
        return 0;
    }
    /* ...Code that doesn't touch s */
    if (s) {
        /* This code is unreachable */
    }
    return 0;
}

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Code Block

bgColor	#ccccff
lang	c

int func(int condition) {
    char *s = NULL;
    if (condition) {
        s = (char *)malloc(10);
        if (s == NULL) {
           /* Handle error */
        }
        /* Process s */
    }
    /* ... Code that doesn't touch s */
    if (s) {
        /* This code is now reachable */
    }
    return 0;
}

...

Code Block

bgColor	#FFCCCC
lang	c

int s_loop(char *s) {
    size_t i;
    size_t len = strlen(s);
    for (i=0; i < len; i++) {
        /* ... Code that doesn't change s, i, or len */
	  if (s[i] == '\0') {
	    /* This code is never reached */
      }
    }
    return 0;
}

...

Code Block

bgColor	#ccccff
lang	c

int s_loop(char *s) {
    size_t i;
    size_t len = strlen(s);
    for (i=0; i < len; i++) {
        /* ... */
	  Code that doesn't change s, i, or len */
	  if (s[i+1] == '\0') {
	    /* This code is now reached */
      }
    }
    return 0;
}

...

Code Block

bgColor	#FFCCCC
lang	c

if (param == 1)
   openWindow();
 else if (param == 2)
   closeWindow();
 else if (param == 1) /* Duplicated condition */
   moveWindowToTheBackground();

Note that duplicating a condition violates this guideline only if the duplicate conditions always behave similarly...see a compliant solution below for a condition that is textually a duplicate but behaves differently.

Compliant Solution (if/else if)

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Code Block

bgColor	#ccccff
lang	c

if (param == 1)
   openWindow();
 else if (param == 2)
   closeWindow();
 else if (param == 3)
   moveWindowToTheBackground();

Noncompliant Code Example (logical operators)

Using the same subexpression on either side of a logical operator is almost always a mistake. In this noncompliant code example, the rightmost subexpression of the controlling expression of each if statement has no effect.

Compliant Solution (Conditional Side-Effects)

This code does not violate this recommendation, because even though the conditions are textually identical, they have different side effects, because the getc() function advances the stream marker.

Code Block

bgColor	#ccccff

Code Block

bgColor	#FFCCCC
lang	c

if (getc(a) == b && a == b) { // if the first one is true, the second one is too
  do_x();
}
if (a == c || a == c ) { // if the first one is true, the second one is too
  do_w();
}

Compliant Solution (logical operators)

':')
   readMoreInput();
 else if (getc() == ':')
   readMoreInput();
 else if (getc() == ':')
   readMoreInput();

Noncompliant Code Example (logical operators)

Using the same subexpression on either side of a logical operator is almost always a mistake. In this noncompliant code exampleIn this compliant solution, the rightmost subexpression of the controlling expression of each if statement has been removedno effect.

Code Block

bgColor	#ccccff#FFCCCC
lang	c

if (a == b && a == b) { // if the first one is true, the second one is too
  do_x();
}
if (a == c || a == c ) { 
  do_w();
}

Noncompliant Code Example (Unconditional Jump)

// if the first one is true, the second one is too
  do_w();
}

Compliant Solution (logical operators)

In this compliant solution, the rightmost subexpression of the controlling expression of each if statement has been removed.Unconditional jump statements typically has no effect.

Code Block

bgColor	#FFCCCC#ccccff
lang	c

#include <stdio.h>
 
for (int i = 0; i < 10; ++iif (a == b) { 
  printf("i is %d", i);
  continue;  // this is meaningless; the loop would continue anyway
}

...

do_x();
}
if (a == c) { 
  do_w();
}

Noncompliant Code Example (Unconditional Jump)

The continue statement has been removed from this compliant solution.Unconditional jump statements typically has no effect.

Code Block

bgColor	#ccccff#FFCCCC
lang	c

#include <stdio.h>
 
for (int i = 0; i < 10; ++i) {
   printf("i is %d", i);
  continue; 
}

Exceptions

  // this is meaningless; the loop would continue anyway
}

Compliant Solution (Unconditional Jump)

The continue statement has been removed from this compliant solution.

Code Block

bgColor	#ccccff
lang	c

#include <stdio.h>
 
for (int i = 0; i < 10; ++i) {
   printf("i is %d", i); 
}

Exceptions

Anchor

	MSC12-EX1
	MSC12-EX1

MSC12 AnchorMSC07-EX1MSC07-EX1MSC07-C-EX1: In some situations, seemingly dead code may make software resilient. An example is the default label in a switch statement whose controlling expression has an enumerated type and that specifies labels for all enumerations of the type. (See MSC01-C. Strive for logical completeness.) Because valid values of an enumerated type include all those of its underlying integer type, unless enumeration constants are provided for all those values, the default label is appropriate and necessary.

Code Block

bgColor	#ccccff
lang	c

typedef enum { Red, Green, Blue } Color;
const char* f(Color c) {
  switch (c) {
    case Red: return "Red";
    case Green: return "Green";
    case Blue: return "Blue";
    default: return "Unknown color";   /* Not dead code */
  }
}

void g() {
  Color unknown = (Color)123;
  puts(f(unknown));
}

Anchor

	MSC12-EX2
	MSC12-EX2

MSC12-EX2: It is permissible to temporarily remove code that may be needed later. (See MSC04-C. Use comments consistently and in a readable fashion for an illustration.)

Anchor

	MSC07MSC12-EX2EX3MSC07
	MSC12-EX2EX3

MSC07MSC12-C-EX2: It is permissible to temporarily remove code that may be needed later. (See MSC04-C. Use comments consistently and in a readable fashion for an illustration.)EX3: Unused functions and variables that are part of an exported library do not violate this guideline. Likewise, code that is never executed because it is #ifdefed out does not violate this guideline, on the grounds that it could be subsequently used in another application, or built on a different platform.

Risk Assessment

The presence of code that has no effect or is never executed can indicate logic errors that may result in unexpected behavior and vulnerabilities. Such code can be introduced into programs in a variety of ways and eliminating it can require significant analysis.

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Tool

Version

Checker

Description

Astrée

Include Page

	Astrée_V
	Astrée_V

dead-assignment
dead-initializer
expression-result-unused
redundant-operation
unreachable-code
unreachable-code-after-jump
unused-functionunreachable-code
statement-sideeffect

Partially Supported + partially checked

CodeSonar

Include Page

	CodeSonar_V
	CodeSonar_V

DIAG.UNEX.*
LANG.STRUCT.EBS
LANG.STRUCT.RC
MISC.NOEFFECT
LANG.STRUCT.ALIGNAS.EZA
LANG.STRUCT.UC
LANG.STRUCT.UA
LANG.STRUCT.UULABEL
LANG.STRUCT.UUMACRO
LANG.STRUCT.UUPARAM
LANG.STRUCT.UUTAG
LANG.STRUCT.UUTYPELANG.STRUCT.UUVAR

Code not exercised by analysis
Empty branch statement checks
Redundant condition
Function call has no effect
Explicit Zero Alignment
Unreachable code checks
Useless assignment
Unused Label
Unused Macro
Unused Parameter
Unused Tag
Unused Type
Unused Variable

Coverity

Include Page

	Coverity_V
	Coverity_V

NO_EFFECT

DEADCODE

UNREACHABLE

Finds statements or expressions that do not accomplish anything or statements that perform an unintended action.

Can detect the specific instance where code can never be reached because of a logical contradiction or a dead "default" in switch statement

Can detect the instances where code block is unreachable because of the syntactic structure of the code

ECLAIR

Include Page

	ECLAIR_V
	ECLAIR_V

CC2.MSC12

Partially implemented

GCC

3.0

-Wunused-value
-Wunused-parameter

Options detect unused local variables, nonconstant static variables and unused function parameters, or unreachable code respectively.function parameters, or unreachable code respectively.

Helix QAC

Include Page

	Helix QAC_V
	Helix QAC_V

C3110, C3112, C3307, C3404, C3426, C3427

Klocwork

Include Page

	Klocwork_V
	Klocwork_V

CWARN.NOEFFECT.SELF_ASSIGN
CWARN.NOEFFECT.UCMP.GE
CWARN.NOEFFECT.UCMP.GE.MACRO
CWARN.NOEFFECT.UCMP.LT
CWARN.NOEFFECT.UCMP.LT.MACRO
CWARN.NULLCHECK.FUNCNAME
EFFECT
INVARIANT_CONDITION.UNREACH
LA_UNUSED
MISRA.STMT.NO_EFFECT
UNREACH.GEN
UNREACH.RETURN
UNREACH.SIZEOF
UNREACH.ENUM
LA_UNUSED
VA_UNUSED.GEN
VA_UNUSED.INIT
INVARIANT_CONDITION.UNREACH

LDRA tool suite

Include Page

	LDRA_V
	LDRA_V

8 D, 65 D, 105 D, I J, 139 S, 140 S, 57 S

Partially implemented

Parasoft C/C++test

Include Page

Parasoft_V Parasoft_V MISRA2004-14_1_a, MISRA2004-14_1_b, MISRA2004-14_1_c, MISRA2004-14_1_d, MISRA2004-14_1_e, MISRA2004-14_1_f, MISRA2004-14_1_g, BD-PB-SWITCH

Polyspace Bug Finder

R2016a

Dead code

Unreachable code

Use of memset with size argument zero

Code does not execute

Default case is missing and may be reached

Size argument of function in memset family is zero

Partially implemented

Parasoft C/C++test

Include Page

	Parasoft_V
	Parasoft_V

CERT_C-MSC12-a
CERT_C-MSC12-b
CERT_C-MSC12-c
CERT_C-MSC12-d
CERT_C-MSC12-e
CERT_C-MSC12-f
CERT_C-MSC12-g
CERT_C-MSC12-h
CERT_C-MSC12-i
CERT_C-MSC12-j
CERT_C-MSC12-k

There shall be no unreachable code in "else" block
There shall be no unreachable code after 'return', 'break', 'continue', and 'goto' statements
There shall be no unreachable code in "if/else/while/for" block
There shall be no unreachable code in switch statement
There shall be no unreachable code in 'for' loop
There shall be no unreachable code after 'if' or 'switch' statement
There shall be no unreachable code after "if" or "switch" statement inside while/for/do...while loop
Avoid switch with unreachable branches
Avoid unreachable methods
Avoid conditions that always evaluate to the same value
All non-null statements shall either have at least one side-effect however executed or cause control flow to change

PC-lint Plus

Include Page

	PC-lint Plus_V
	PC-lint Plus_V

438, 474, 505, 522, 523,
527, 528, 529, 563, 612,
714, 715, 719, 749, 750,
751, 752, 753, 754, 755,
756, 757, 758, 768, 769,
774, 827, 838, 1972

Fully supported

Polyspace Bug Finder

Include Page

	Polyspace Bug Finder_V
	Polyspace Bug Finder_V

CERT C: Rec. MSC12-C

Checks for:

Unreachable code
Dead code

Rec. partially covered.

PRQA QA-C

Include Page

PRQA QA-C_v

3426, 3427, 3307, 3110, 3112, 3404, 1501, 1503, 2008, 2880, 2881, 2882, 2883, 2877, 3196, 3202, 3203, 3205, 3206, 3207, 3210, 3219, 3229, 3404, 3422, 3423, 3425, 3470, 2980, 2981, 2982, 2983, 2984, 2985, 2986

Partially implemented

RuleChecker

Include Page

	RuleChecker_V
	RuleChecker_V

dead-assignment
dead-initializer
expression-result-unused
redundant-operation
unreachable-code-after-jump
unused-function
statement-sideeffect

Partially checked

SonarQube C/C++ Plugin

Include Page

	SonarQube C/C++ Plugin_V
	SonarQube C/C++ Plugin_V

S1764, S2589, S2583, S1116, S1172, S1763, S1862, S1065, S1656, S2754, S1751

Splint

Include Page

	Splint_V
	Splint_V

-standard

The default mode checks for unreachable code.

PVS-Studio

6.22

Include Page

	PVS-Studio_V
	PVS-Studio_V

V551, V606, V649, V779

Related Vulnerabilities

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

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Versions Compared

Old Version 120

New Version Current

Key

Compliant Solution (if/else if)

Noncompliant Code Example (logical operators)

Compliant Solution (Conditional Side-Effects)

Compliant Solution (logical operators)

Noncompliant Code Example (logical operators)

Noncompliant Code Example (Unconditional Jump)

Compliant Solution (logical operators)

Noncompliant Code Example (Unconditional Jump)

Exceptions

Compliant Solution (Unconditional Jump)

Exceptions

Risk Assessment

Related Vulnerabilities