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Attempting to access an object outside of its lifetime can result in an exploitable vulnerability.

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Noncompliant Code Example (Static Variables)

This non-compliant noncompliant code example declares the variable p as a pointer to a constant char with file scope. The value of str is assigned to p within the dont_do_this() function. However, str has automatic storage duration, so the lifetime of str ends when the dont_do_this() function exits.

const char const *p;
void dont_do_this(void) {
    const char const str[] = "This will change";
    p = str; /* dangerous */
    /* ... */
}

void innocuous(void) {
    const char const str[] = "Surprise, surprise";
}
/* ... */
dont_do_this();
innocuous();
/* p might be pointing to "Surprise, surprise" */

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void this_is_OK(void) {
    const char const str[] = "Everything OK";
    const char const *p = str;
    /* ... */
}
/* p is inaccessible outside the scope of string str */

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If it is necessary for p to be defined with file scope, it can be set to NULL before str is destroyed. This prevents p from taking on an indeterminate value, although any references to p must check for NULL.

const char const *p;
void is_this_OK(void) {
    const char const str[] = "Everything OK?";
    p = str;
    /* ... */
    p = NULL;
}

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Noncompliant Code Example (Return Values)

In this example, the function init_array() incorrectly returns a pointer to a local stack variable.

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Some compilers generate a warning when a pointer to an automatic variable is returned from a function, as in this example. Compile your code at high warning levels and resolve any warnings (see MSC00-AC. Compile cleanly at high warning levels).

Compliant Solution (Return Values)

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