SEI CERT C Coding Standard

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changes.mady.by.user Joerg Herter

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changes.mady.by.user Caden Milne

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Comment: Changed C24 -> C23

The C11 C23 Standard requires type specifiers and forbids implicit function declarations. The C90 Standard allows implicit typing of variables and functions. Consequently, some existing legacy code uses implicit typing. Some C compilers still support legacy code by allowing implicit typing, but it should not be used for new code. Such an implementation may choose to assume an implicit declaration and continue translation to support existing programs that used this feature.

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C no longer allows the absence of type specifiers in a declaration. The C Standard, 6.7.3 paragraph 2 [ ISO/IEC 9899:20112024 ], states

At Except where the type is inferred (6.7.10), at least one type specifier shall be given in the declaration specifiers in each declaration, and in the specifier-qualifier list in each struct member declaration and type name.

This noncompliant code example omits the type specifier:

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MISRA 2012 Rule 8.1 

MISRA C:2012 Rule 17.3

Types shall be

A function shall not be declared implicitly

PRQA QA-CPRQA QACvPRQA QACvFully implemented

Tool

Version

Checker

Description

Astrée
Include Page
Astrée_V
Astrée_V

type-specifier

function-return-type

implicit-function-declaration

undeclared-parameter

Fully checked
Axivion Bauhaus Suite

Include Page
Axivion Bauhaus Suite_V
Axivion Bauhaus Suite_V

CertC-DCL31Fully implemented
Clang
Include Page
Clang_V
Clang_V
-Wimplicit-int
Compass/ROSE




Coverity
Include Page
Coverity_V
Coverity_V
MISRA C 2012 Rule 8.1Implemented
Cppcheck Premium

Include Page
Cppcheck Premium_V
Cppcheck Premium_V

premium-cert-dcl31-cPartially Implemented
Can detect implicit int

ECLAIR

Include Page
ECLAIR_V
ECLAIR_V

CC2.DCL31

Fully implemented

GCC
Include Page
GCC_V
GCC_V


Can detect violations of this rule when the -Wimplicit and -Wreturn-type flags are used

Helix QAC

Include Page
Helix QAC_V
Helix QAC_V

C0434, C2050, C2051, C3335Fully implemented
Klocwork
Include Page
Klocwork_V
Klocwork_V

CWARN.IMPLICITINT
FUNCRET.IMPLICIT
MISRA.DECL.NO_TYPE
MISRA.FUNC.NOPROT.CALL
RETVOID.IMPLICIT

Fully implemented

LDRA tool suite
Include Page
LDRA_V
LDRA_V

24 D, 41 D, 20 S, 326 S, 496 S

Fully implemented

Parasoft C/C++test
Include Page
Parasoft_V
Parasoft_V
CERT_C-DCL31-a
All functions shall be declared before use
PC-lint Plus

Include Page
PC-lint Plus_V
PC-lint Plus_V

601, 718, 746, 808

Fully supported

Polyspace Bug Finder

Include Page
Polyspace Bug Finder_V
Polyspace Bug Finder_V

CERT C:

Rule DCL31-C


Checks for:

  • Types not
  • explicitly specified
  • Implicit function declaration

Rule fully covered.

PVS-Studio

Include Page

PVS-

Studio_

V

PVS-

Studio_

0434 (C)
1302
2050
2051
3335

V

V1031
SonarQube C/C++ Plugin
Include Page
SonarQube C/C++ Plugin_V
SonarQube C/C++ Plugin_V
 S819, S820  Partially implemented; implicit return type not covered.
RuleChecker
Include Page
RuleChecker_V
RuleChecker_V

type-specifier

function-return-type

implicit-function-declaration

undeclared-parameter

Fully checked
TrustInSoft Analyzer

Include Page
TrustInSoft Analyzer_V
TrustInSoft Analyzer_V

type specifier missing

Partially verified (exhaustively detects undefined behavior).

Related Vulnerabilities

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

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[ISO/IEC 9899:1990]
[ISO/IEC 9899:20112024]Subclause 6.7.23, "Type Specifiers"
[Jones 2008]

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