Page History

Opening Use opening and closing braces for if, for, or and while statements should always be used, even if when the statement's body contains only a single statement.If an if, while, or for statement is used in a macro, the macro definition should not conclude with a semicolon. (See recommendation PRE11-C. Do not conclude macro definitions with a semicolon. ) Braces improve the uniformity and readability of code.

More importantly, when inserting an additional statement important, it is easy to forget to add braces when inserting additional statements into a body containing only a single statement, it is easy to forget to add braces because the conventional indentation gives strong (but misleading) guidance to the structure.

Braces also help ensure that macros with multiple statements are properly expanded. Such a macro should be wrapped in a do-while loop. (See recommendation PRE10-C. Wrap multi-statement macros in a do-while loop.) However, when the do-while loop is not present, braces can still ensure that the macro expands as intended.

Noncompliant Code Example

This noncompliant code example uses authenticates a user with an if statement without braces to authenticate a user.that lacks braces:

Code Block

bgColor	#ffcccc


int login;

if (invalid_login())
  login = 0;
else
  login = 1;

A developer might This program behaves as expected. However, a maintainer might subsequently add a debugging statement to determine when the login is valid, debug statement or other logic but forget to add opening and closing braces.:

Code Block

bgColor	#ffcccc


int login;

if (invalid_login())
  login = 0;
else
  // Debug line added below
  printfSystem.out.println("Login is valid\n");
  /*/ The debuggingnext line addedis always hereexecuted */
  login login = 1;                   /* this line always gets executed, regardless of a valid login! */

The code's indentation disguises the functionality of the programDue to the indentation of the code, it is difficult to tell that the code will not function as intended by the programmer, potentially leading to a security breach.

Compliant Solution

In the This compliant solution , uses opening and closing braces are used even when though the body is a single statement.of the if and else bodies of the if statement are single statements:

Code Block

bgColor	#CCCCFF


int login;

if (invalid_login()) {
  login = 0;
} else {
  login = 1;
}

Noncompliant Code Example

This noncompliant code example has nests an if statement nested in within another if statement, without braces around the if and else bodies.:

Code Block

bgColor	#ffcccc


int privileges;

if (invalid_login())
  if (allow_guests())
    privileges = GUEST;
else
  privileges = ADMINISTRATOR;

The indentation could might lead the programmer to believe that a user is given users are granted administrator privileges only when the user's their login is valid. However, the else statement actually attaches binds to the inner if statement:

Code Block

bgColor	#ffcccc


int privileges;

if (invalid_login())
  if (allow_guests())
    privileges = GUEST;
  else
    privileges = ADMINISTRATOR;

This is a security loophole: users with invalid logins can still Consequently, this defect allows unauthorized users to obtain administrator privileges.

Compliant Solution

In the This compliant solution , adding uses braces removes to remove the ambiguity and ensures , consequently ensuring that privileges are correctly assigned.:

Code Block

bgColor	#CCCCFF


int privileges;

if (invalid_login()) {
  if (allow_guests()) {
    privileges = GUEST;
  } 
} else {
  privileges = ADMINISTRATOR;
}

Risk Assessment

Recommendation	Severity	Likelihood	Remediation Cost	Priority	Level
EXP19-C	medium	probable	medium	P8	L2

Related Guidelines

ISO/IEC 9899:1999 Section 6.8.4, "Selection statements"

MISRA Rule 14.8

Bibliography

Wiki Markup
\[[GNU 2010\|AA. Bibliography#GNU 10]\] [Coding Standards, Section 5.3, "Clean Use of C Constructs"\|http://www.gnu.org/prep/standards/standards.html#Syntactic-Conventions]