SEI CERT C Coding Standard

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Do not use a semicolon on the same line as an if, for, or while statement because it typically indicates programmer error and can result in unexpected behavior.

Noncompliant Code Example

In this noncompliant code example, a semicolon is used on the same line as an if statement:

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

Compliant Solution

It is likely, in this example, that the semicolon was accidentally inserted:

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

Risk Assessment

Errors of omission can result in unintended program flow.

Recommendation

Severity

Likelihood

Remediation Cost

Priority

Level

EXP15-C

High

Likely

Low

P27

L1


Automated Detection

Tool

Version

Checker

Description

Astrée
24.04
empty-bodyFully checked
Axivion Bauhaus Suite

7.2.0

CertC-EXP15Fully implemented
CodeSonar
8.1p0
LANG.STRUCT.EBSEmpty branch statement
Helix QAC

2024.3

C3109
Klocwork
2024.3

SEMICOL


LDRA tool suite
9.7.1
11 S, 12 S, 428 SFully Implemented
Parasoft C/C++test

2023.1

CERT_C-EXP15-aSuspicious use of semicolon
PC-lint Plus

1.4

721, 722

Partially supported: reports missing body from if, for, or while with semi-colon immediately following predicate

Polyspace Bug Finder

R2024a

CERT C: Rec. EXP15-CChecks for semicolon on same line as for, if or while statement (rule fully covered)
PVS-Studio

7.33

V529, V715
SonarQube C/C++ Plugin
3.11
S1116
RuleChecker
24.04
empty-bodyFully checked

Related Guidelines

SEI CERT Oracle Coding Standard for JavaMSC51-J. Do not place a semicolon immediately following an if, for, or while condition
ISO/IEC TR 24772:2013Likely Incorrect Expression [KOA]
MITRE CWECWE-480, Use of incorrect operator

Bibliography

[Hatton 1995]Section 2.7.2, "Errors of Omission and Addition"


4 Comments

  1. Robert Seacord (Manager)

    This guideline seems way too strict. For example, I see nothing wrong with the following example:

    if ( x ) y++;

    Notice this example is nonconforming because a semicolon appears on the same line as the if.

  2. Robert Seacord (Manager)

    I think this guideline should be eliminated and the example integrated with MSC12-C. Detect and remove code that has no effect

    1. Martin Sebor

      I agree that this is draconian. I suspect the intent is to prevent problems such as:

      char* strchr(const char *str, int c) {
  for (; *str; ++str);   /* <<< forgot to remove semicolon */
    if ((unsigned char)*str == c)
      return str;
  return NULL;
}

      that are sometimes introduced by copying and pasting, for instance from code such as:

      size_t strlen(const char *str) {
  const char *s = str;
  for (; *str; ++str);
  return (size_t)(str - s);
}

      (Note the strchr() implementation above is buggy in another way that's unrelated to the semicolon.)

  3. Olivera Holzkamp

    There is no  risk assesment for this recommendation