Why Does Function Overload Cause an Error with the Most Negative Integer Value?

Ambiguous Function Overload Errors with Negative Integer Values

When overloading functions in C , it's crucial to understand the specific requirements and limitations of negative integer literals. Consider the following example:

<code class="cpp">void display(int a) { cout &lt;&lt; &quot;int&quot; &lt;&lt; endl; }
void display(unsigned a) { cout &lt;&lt; &quot;unsigned&quot; &lt;&lt; endl; }

int main() {
    int i = -2147483648;
    cout &lt;&lt; i &lt;&lt; endl; // prints -2147483648
    display(-2147483648); // compilation error
}

One might expect that any integer value would call display(int), while values outside the int range would be ambiguous. However, the compilation error occurs specifically when using the most negative int value, -2147483648.

Why the Error Occurs

The key lies in the absence of negative integer literals in C . Integer literals cannot start with a "-" sign, meaning -2147483648 is interpreted as the unary negation operator applied to 2147483648.

Since 2147483648 exceeds the int range, it's automatically promoted to a long int. The ambiguity arises when display(-2147483648) is invoked: the compiler cannot determine whether to call display(int) or display(long int).

Exception Handling

This behavior is observed when the negative number and its positive representation have the same binary value, such as with -32768 for a short.

Avoiding Ambiguity

To avoid ambiguity, consider the following best practices:

• Use std::numeric_limits to retrieve the minimum and maximum values for a type portably:
  std::numeric_limits<type>::min();
• Explicitly cast negative values to the desired type:
  display(static_cast<int>(-2147483648));

By adhering to these guidelines, you can prevent ambiguity and ensure that your code functions as intended.

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