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In this example, is_ptr(e) returns true if expression e has a pointer type. is_ptr(e) calls variadic function isPtr(...), but the call takes place in a sizeof expression. Consequently, isPtr(...) must be declared, but it need not, and should not, be defined.

Non-compliant Code Example

This example uses a variadic function to concatenate an arbitrary number of null-terminated character sequences (NTCS) in a single NTCS. Each call to the function must use a null pointer value to mark the end of the argument list.

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char *u = concatenate("hello", separator, "world"); // undefined behavior

char *v = concatenate("hello", ' ', "world", NULL); // undefined behavior

Compliant Solution

Rather than use a variadic function, you can use a chain of binary operations:

#include <string>

string separator = /* some reasonable value */;

string s = "hello" + separator + "world";

Risk Assessment

Incorrectly using a variadic function can result in abnormal program termination, unintended information disclosure, or execution of arbitrary code.

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