The sizeof operator yields the size (in bytes) of its operand, which may can be an expression or the parenthesized name of a type. However, using the sizeof operator to determine the size of arrays is error prone.
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In this noncompliant code example, the function {{clear()}} zeros the elements in an array. The function has one parameter declared as {{int array\[\]}} and is passed a static array consisting of 12 {{int}} as the argument. The function {{clear()}} uses the idiom {{sizeof(array) / sizeof(array\[0\])}} to determine the number of elements in the array. However, {{array}} has a pointer type because it is a parameter. As a result, {{sizeof(array)}} is equal to the {{sizeof(int \*)}}. For example, on an architecture (such as IA-32) where the {{sizeof(int) == 4}} and the {{sizeof(int *) == 4}}, the expression {{sizeof(array) / sizeof(array\[0\])}} evaluates to 1, regardless of the length of the array passed, leaving the rest of the array unaffected. |
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Search for vulnerabilities resulting from the violation of this rule on the CERT website.
Related Guidelines
CERT C++ Secure Coding Standard: ARR01-CPP. Do not apply the sizeof operator to a pointer when taking the size of an array
Bibliography
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\[[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\] Section 6.7.5.2, "Array declarators"
MITRE CWE: CWE-467, "Use of sizeof() on a Pointer Type"
Bibliography
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declarators" \[[Drepper 2006|AA. Bibliography#Drepper 06]\] Section 2.1.1, "Respecting Memory Bounds" \[[MITRE 2007|AA. Bibliography#MITRE 07]\] [CWE ID 467|http://cwe.mitre.org/data/definitions/467.html], "Use of sizeof() on a Pointer Type" |
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06. Arrays (ARR) ARR02-C. Explicitly specify array bounds, even if implicitly defined by an initializer