SEI CERT C Coding Standard

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The atoi(), atol(), atoll(), and atof() functions convert the initial portion of a string token to int, long int, long long int, and double representation, respectively. Except for the behavior on error ([ISO/IEC 9899:2024], s7.24.1.2), they are equivalent to

Code Block
atoi: (int)strtol(nptr, (char **)NULL, 10)
atol: strtol(nptr, (char **)NULL, 10)
atoll: strtoll(nptr, (char **)NULL, 10)
atof: strtod(nptr, (char **)NULL)

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  • do not need to set errno on an error;
  • have undefined behavior 16 if the value of the result cannot be represented;
  • return 0 (or 0.0) if the string does not represent an integer (or decimal), which is indistinguishable from a correctly formatted, zero-denoting input string.

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Recommendation

Severity

Likelihood

Detectable

RepairableRemediation Cost

Priority

Level

ERR34-C

Medium

Unlikely

Yes

YesMedium

P4P6

L3L2

Automated Detection

Tool

Version

Checker

Description

Axivion Bauhaus Suite

Include Page
Axivion Bauhaus Suite_V
Axivion Bauhaus Suite_V

CertC-ERR34
Clang
Include Page
Clang_39_V
Clang_39_V
cert-err34-cChecked by clang-tidy
CodeSonar
Include Page
CodeSonar_V
CodeSonar_V

BADFUNC.ATOF
BADFUNC.ATOI
BADFUNC.ATOL
BADFUNC.ATOLL

(customization)

Use of atof
Use of atoi
Use of atol
Use of atoll

Users can add custom checks for uses of other undesirable conversion functions.

Compass/ROSE



Can detect violations of this recommendation by flagging invocations of the following functions:

    • atoi()
    • scanf(), fscanf(), sscanf()
    • Others?
Helix QAC

Include Page
Helix QAC_V
Helix QAC_V

C5030

C++5016


Klocwork
Include Page
Klocwork_V
Klocwork_V

CERT.ERR.CONV.STR_TO_NUM
MISRA.STDLIB.ATOI
SV.BANNED.RECOMMENDED.SCANF


LDRA tool suite
Include Page
LDRA_V
LDRA_V

44 S

Fully implemented

Parasoft C/C++test
Include Page
Parasoft_V
Parasoft_V

CERT_C-ERR34-a

The library functions 'atof', 'atoi and atol from library ', 'atol' and 'atoll' functions from the 'stdlib.h shall ' or 'cstdlib' library should not be used
PC-lint Plus

Include Page
PC-lint Plus_V
PC-lint Plus_V

586

Assistance provided

Polyspace Bug Finder

Include Page
Polyspace Bug Finder_V
Polyspace Bug Finder_V

CERT C: Rule ERR34-CChecks for unsafe conversion from string to numeric value (rule fully covered)
SonarQube C/C++ Plugin
Include Page
SonarQube C/C++ Plugin_V
SonarQube C/C++ Plugin_V
S989

...

CWE-391 = Union( ERR34-C, list) where list =


  • Failure to errors outside of string-to-number conversion functions


CWE-676 and ERR34-C


  • Independent( ENV33-C, CON33-C, STR31-C, EXP33-C, MSC30-C, ERR34-C)



  • ERR34-C implies that string-parsing functions (eg atoi() and scanf()) are dangerous.



  • CWE-676 = Union( ERR34-C, list) where list =



  • Invocation of dangerous functions besides the following:



  • atoi(), atol(), atoll(), atof(), The scanf()family


CWE-758 and ERR34-C

Independent( INT34-C, INT36-C, MSC37-C, FLP32-C, EXP33-C, EXP30-C, ERR34-C, ARR32-C)

Intersection( CWE-758, ERR34-C) =


  • Undefined behavior arising from a non-representable numeric value being parsed by an ato*() or scanf() function


CWE-758 – ERR34-C =


  • Undefined behavior arising from using a function outside of the ato*() or scanf() family


ERR34-C – CWE-758 =


  • The ato*() or scanf() family receives input that is not a number when trying to parse one


Bibliography

[ISO/IEC 9899:2024]Subclause 7.24.1, "Numeric conversion functions"
[Klein 2002]

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