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This non-compliant 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.
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char const char *p; void dont_do_this() { char const char str[] = "This will change"; p = str; /* dangerous */ /* ... */ } void innocuous() { char const char str[] = "Surprise, surprise"; } /* ... */ dont_do_this(); innocuous(); /* now, it is likely that p is pointing to "Surprise, surprise" */ |
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void this_is_OK() {
char const char str[] = "Everything OK";
char const char *p = str;
/* ... */
}
/* pointer p is now 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.
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char const char *p; void is_this_OK() { char const char str[] = "Everything OK?"; p = str; /* ... */ p = NULL; } |
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