Synopsis

Do not read uninitialized memory.

Enabled by default

Yes

Severity/Certainty

High/Medium

Full description

Uninitialized automatic variables or dynamically allocated memory has indeterminate values, which for objects of some types, can be a trap representation. Reading such trap representations is undefined behavior; it can cause a program to behave in an unexpected manner and provide an avenue for attack.

Coding standards

Code examples

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

#define NULL 0
void set_flag(int number, int *sign_flag) {
    if (NULL == sign_flag) {
        return;
    }

    if (number > 0) {
        *sign_flag = 1;
    } else if (number < 0) {
        *sign_flag = -1;
    }
}

int is_negative(int number) {
    int sign;
    set_flag(number, &sign);
    return sign < 0;
}

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

#define NULL 0
void set_flag(int number, int *sign_flag) {
    if (NULL == sign_flag) {
        return;
    }

    /* Account for number being 0 */
    if (number >= 0) {
        *sign_flag = 1;
    } else {
        *sign_flag = -1;
    }
}

int is_negative(int number) {
    int sign = 0; /* Initialize for defense-in-depth */
    set_flag(number, &sign);
    return sign < 0;
}