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Violations of this guidelines are indicated when a pointer to an array is added to the result of the {{sizeof}} operator or {{offsetof}} macro which return a size and offset, respectively. However, adding an array pointer to the number of array elements, for example by using the {{arr\[sizeof(arr)/sizeof(arr\[0\])\])}} idiom, is allowed, provided that {{arr}} refers to an array and not a pointer. |
Noncompliant Code Example
In this noncompliant code example, the pointer buf is added to sizeof(buf). This is noncompliant because sizeof(buf) is scaled by int and is scaled again when added to buf.
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int buf[INTBUFSIZE];
int *buf_ptr = buf;
while (havedata && buf_ptr < (buf + sizeof(buf))) {
*buf_ptr++ = parseint(getdata);
}
|
Noncompliant Code Example
In this noncompliant code example, skip is added to the pointer s. However, skip represents the byte offset of ull_2 in struct big. When added to s, skip is scaled by the size of struct big.
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struct big {
unsigned long long ull_1; /* typically 8 bytes */
unsigned long long ull_2; /* typically 8 bytes */
unsigned long long ull_3; /* typically 8 bytes */
int si_4; /* typically 4 bytes */
int si_5; /* typically 4 bytes */
};
/* ... */
size_t skip = offsetof(struct big, ull_2);
struct big *s = (struct big *)malloc(sizeof(struct big));
if (!s) {
/* Handle malloc error */
}
memset(s + skip, 0, sizeof(struct big) - skip);
/* ... */
free(s);
s = NULL;
|
Noncompliant Code Example
In this noncompliant code example, wcslen(error_msg) * sizeof(wchar_t) bytes are scaled by the size of wchar_t when added to error_msg.
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/* ... */
wchar_t error_msg[WCHAR_BUF];
wcscpy(error_msg, L"Error: ");
fgetws(error_msg + wcslen(error_msg) * sizeof(wchar_t), WCHAR_BUF - 7, stdin);
/* ... */
|
Bibliography
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\[[Dowd 06|AA. Bibliography#Dowd 06]\] Chapter 6, "C Language Issues"
\[[ISO/IEC PDTR 24772|AA. Bibliography#ISO/IEC PDTR 24772]\] "HFC Pointer casting and pointer type changes" and "RVG Pointer Arithmetic"
\[[MISRA 04|AA. Bibliography#MISRA 04]\] Rules 17.1-17.4
\[[MITRE 07|AA. Bibliography#MITRE 07]\] [CWE ID 468|http://cwe.mitre.org/data/definitions/468.html], "Incorrect Pointer Scaling"
\[[Murenin 07|AA. Bibliography#Murenin 07]\] |
