...
| Code Block | ||||
|---|---|---|---|---|
| ||||
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;
}
|
...
| Code Block | ||||
|---|---|---|---|---|
| ||||
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 | ||||
|---|---|---|---|---|
| ||||
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 | ||||
|---|---|---|---|---|
| ||||
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 | ||||
|---|---|---|---|---|
| ||||
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)
...
| Code Block | ||||
|---|---|---|---|---|
| ||||
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 | ||||
|---|---|---|---|---|
| ||||
| Code Block | ||||
| ||||
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 | ||||
|---|---|---|---|---|
| ||||
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();// if the first one is true, the second one is too do_w(); } |
Noncompliant Code Example (Unconditional Jump)
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 | ||||
|---|---|---|---|---|
| ||||
#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 | ||||
|---|---|---|---|---|
| ||||
#include <stdio.h>
for (int i = 0; i < 10; ++i) {
printf("i is %d", i);
continue; // this is meaningless; the loop would continue anyway
}
|
Compliant Solution (Unconditional Jump)
The continue statement has been removed from this compliant solution.
| Code Block | ||||
|---|---|---|---|---|
| ||||
#include <stdio.h>
for (int i = 0; i < 10; ++i) {
printf("i is %d", i);
}
|
Exceptions
| Anchor | ||||
|---|---|---|---|---|
|
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....
Tool | Version | Checker | Description | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Astrée |
| dead-assignment | Partially Supported + partially checked | ||||||||||||||||||
| CodeSonar |
| DIAG.UNEX.* | Code not exercised by analysis | ||||||||||||||||||
| 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 Can detect the instances where code block is unreachable because of the syntactic structure of the code | |||||||||||||||||||
| CC2.MSC12 | Partially implemented | |||||||||||||||||||
| GCC | 3.0 | Options detect unused local variables, nonconstant static variables and unused function parameters, or unreachable code respectively.unused function parameters, or unreachable code respectively. | |||||||||||||||||||
| Helix QAC |
| C3110, C3112, C3307, C3404, C3426, C3427 | |||||||||||||||||||
| Klocwork |
| 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 |
| 8 D, 65 D, 105 D, I J, 139 S, 140 S, 57 S | Partially implemented | ||||||||||||||||||
| Parasoft C/C++test |
| CERT_C-MSC12-a | There shall be no unreachable code in "else" block | ||||||||||||||||||
| PC-lint Plus |
| 438, 474, 505, 522, 523, | Fully supported | ||||||||||||||||||
| Polyspace Bug Finder |
| Checks for:
Rec. partially covered. | Polyspace Bug Finder | ||||||||||||||||||
| Include Page | Polyspace Bug Finder_V | Polyspace Bug Finder_V | Code does not execute Default case is missing and may be reached Size argument of function in A project shall not contain unreachable code There shall be no dead code | PRQA QA-C | |||||||||||||||||
| Include Page | PRQA QA-C_v | 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 |
| dead-assignment | Partially checked | ||||||||||||||||||
| SonarQube C/C++ Plugin |
| S1764, S2589, S2583, S1116, S1172, S1763, S1862, S1065, S1656, S2754, S1751 | |||||||||||||||||||
| Splint |
| | The default mode checks for unreachable code. | ||||||||||||||||||
| V551, V606, V649, V779 |
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
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