bugprone-suspicious-memset-usage

This check finds memset() calls with potential mistakes in their arguments. Considering the function as void* memset(void* destination, int fill_value, size_t byte_count), the following cases are covered:

Case 1: Fill value is a character ``'0'``

Filling up a memory area with ASCII code 48 characters is not customary, possibly integer zeroes were intended instead. The check offers a replacement of '0' with 0. Memsetting character pointers with '0' is allowed.

Case 2: Fill value is truncated

Memset converts fill_value to unsigned char before using it. If fill_value is out of unsigned character range, it gets truncated and memory will not contain the desired pattern.

Case 3: Byte count is zero

Calling memset with a literal zero in its byte_count argument is likely to be unintended and swapped with fill_value. The check offers to swap these two arguments.

Corresponding cpplint.py check name: runtime/memset.

Examples:

void foo() {
  int i[5] = {1, 2, 3, 4, 5};
  int *ip = i;
  char c = '1';
  char *cp = &c;
  int v = 0;

  // Case 1
  memset(ip, '0', 1); // suspicious
  memset(cp, '0', 1); // OK

  // Case 2
  memset(ip, 0xabcd, 1); // fill value gets truncated
  memset(ip, 0x00, 1);   // OK

  // Case 3
  memset(ip, sizeof(int), v); // zero length, potentially swapped
  memset(ip, 0, 1);           // OK
}