Synopsis

Do not access a volatile object through a nonvolatile reference.

Enabled by default

Yes

Severity/Certainty

Low/High

Full description

An object that has volatile-qualified type may be modified in ways unknown to the implementation or have other unknown side effects. Referencing a volatile object by using a non-volatile lvalue is undefined behavior.

Coding standards

Code examples

The following code example fails the check and will give a warning:

#include <stdio.h>

void func(void) {
    static volatile int **ipp;
    static int *ip;
    static volatile int i = 0;

    printf("i = %d.\n", i);

    ipp = &ip; /* May produce a warning diagnostic */
    ipp = (int**) &ip; /* Constraint violation; may produce a warning diagnostic */
    *ipp = &i; /* Valid */
    if (*ip != 0) { /* Valid */
        /* ... */
    }
}

The following code example passes the check and will not give a warning about this issue:

#include <stdio.h>

void func(void) {
    static volatile int **ipp;
    static volatile int *ip;
    static volatile int i = 0;

    printf("i = %d.\n", i);

    ipp = &ip;
    *ipp = &i;
    if (*ip != 0) {
        /* ... */
    }

}