readability-non-const-parameter

The check finds function parameters of a pointer type that could be changed to point to a constant type instead.

When const is used properly, many mistakes can be avoided. Advantages when using const properly:

• prevent unintentional modification of data;

• get additional warnings such as using uninitialized data;

• make it easier for developers to see possible side effects.

This check is not strict about constness, it only warns when the constness will make the function interface safer.

// warning here; the declaration "const char *p" would make the function
// interface safer.
char f1(char *p) {
  return *p;
}

// no warning; the declaration could be more const "const int * const p" but
// that does not make the function interface safer.
int f2(const int *p) {
  return *p;
}

// no warning; making x const does not make the function interface safer
int f3(int x) {
  return x;
}

// no warning; Technically, *p can be const ("const struct S *p"). But making
// *p const could be misleading. People might think that it's safe to pass
// const data to this function.
struct S { int *a; int *b; };
int f3(struct S *p) {
  *(p->a) = 0;
}

// no warning; p is referenced by an lvalue.
void f4(int *p) {
  int &x = *p;
}