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In this noncompliant code example, a pointer is set to reference the start of an array. Array elements are accessed sequentially within the for loop. The array pointer ip is incremented on each iteration.

int ar[20];

for (int *ip = &ar[0]; ip < &ar[21]; ip++) {
  *ip = 0;
}

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This compliant solution fixes the problem from the previous noncompliant code example by using the common idiom {{sizeof(ar)/sizeof(ar\[0\])}} to determine the actual number of elements in the array.  This idiom works only when the definition of the array is visible (see [ARR01-CPP. Do not apply the sizeof operator to a pointer when taking the size of an array]).

int ar[20];

for (int *ip = &ar[0]; ip < &ar[sizeof(ar)/sizeof(ar[0])]; ip++) {
  *ip = 0;
}

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In this noncompliant code example, an iterator is set to reference the beginning of a vector. Vector elements are accessed sequentially within the for loop. The iterator ip is incremented on each iteration.

vector<int> ar( 20, 0);
vector<int>::iterator ip = ar.begin();
for (int i = 1; i <= 22; i++) {
  *ip++ = 1;
}

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This compliant solution fixes the problem from the previous noncompliant code example by using the ranges ar.begin() and ar.end() to determine how many iterations should be executed.

vector<int> ar( 20, 0);
for (vector<int>::iterator ip = ar.begin(); ip < ar.end(); ip++) {
  *ip++ = 1;
}

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In this noncompliant code example, the programmer is trying to determine if a pointer added to a length will wrap around the end of memory.

char *buf;
size_t len = 1 << 30;

/* Check for overflow */
if (buf + len < buf) {
  len = -(size_t)buf-1;
}

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In this compliant solution, both references to buf are cast to size_t. Because {[size_t}} is an unsigned type, C++2003 guarantees that it has modulo behavior.

char *buf;
size_t len = 1 << 30;

/* Check for overflow */
if ((size_t)buf+len < (size_t)buf) {
  len = -(size_t)buf-1;
}

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Another interesting case is shown in this noncompliant code example. The expression buf + n may wrap for large values of n, resulting in undefined behavior.

int process_array(char *buf, size_t n) {
  return buf + n < buf + 100;
}

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In this compliant solution, the "optimization" is performed by hand.

int process_array(char *buf, size_t n) {
  return n < 100;
}

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