SEI CERT C Coding Standard

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Comment: Referenced UB21 of Annex J.

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The only value that can be considered interchangeable between pointers and integers is the constant 0. Except in this case, conversions between integers and pointers may have undesired consequences depending on the [implementation|BB. Definitions#implementation].  According to C99 \[[ISO/IEC 9899:1999|AA. References#ISOBibliography#ISO/IEC 9899-1999]\]:

An integer may be converted to any pointer type. Except as previously specified, the result is implementation defined, might not be correctly aligned, might not point to an entity of the referenced type, and might be a trap representation.

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\[[ISO/IEC 9899:1999|AA. References#ISOBibliography#ISO/IEC 9899-1999]\] Section 6.3.2.3, "Pointers"
\[[ISO/IEC PDTR 24772|AA. References#ISOBibliography#ISO/IEC PDTR 24772]\] "HFC Pointer casting and pointer type changes"
\[[MITRE 07|AA. References#MITREBibliography#MITRE 07]\] [CWE ID 466|http://cwe.mitre.org/data/definitions/466.html], "Return of Pointer Value Outside of Expected Range," and [CWE ID 587|http://cwe.mitre.org/data/definitions/587.html], "Assignment of a Fixed Address to a Pointer"

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