Synopsis

Guarantee that library functions do not form invalid pointers.

Enabled by default

Yes

Severity/Certainty

High/High

Full description

C library functions that make changes to arrays or objects take at least two arguments: a pointer to the array or object and an integer indicating the number of elements or bytes to be manipulated. Supplying arguments to such a function might cause the function to form a pointer that does not point into or just past the end of the object, resulting in undefined behavior.

Coding standards

Code examples

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

#include <stdint.h>
#include <stdio.h>

struct obj {
    char c;
    long long i;
};

void func(FILE *f, struct obj *objs, size_t num_objs) {
    const size_t obj_size = 16;
    if (num_objs > (SIZE_MAX / obj_size) ||
        num_objs != fwrite(objs, obj_size, num_objs, f)) {
        /* Handle error */
    }
}

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

#include <stdint.h>
#include <stdio.h>

struct obj {
    char c;
    long long i;
};

void func(FILE *f, struct obj *objs, size_t num_objs) {
    const size_t obj_size = sizeof *objs;
    if (num_objs > (SIZE_MAX / obj_size) ||
        num_objs != fwrite(objs, obj_size, num_objs, f)) {
        /* Handle error */
    }
}