Why Choose `const char * const` over `const char *` in C ?

const char * const versus const char * in C

A common question arises when examining code utilizing constant character pointers: why use const char * const over const char *? Let's explore this using an example code:

<code class="cpp">void print_string(const char * the_string)
{
    cout << the_string << endl;
}

int main () {
    print_string("What's up?");
}</code>

Here, two options arise for the parameter to print_string: const char * and const char * const. The distinction between them lies in their pointer mutability.

• const char *: While the string it points to is immutable, the pointer itself can be modified to refer to a different string.
• const char * const: Both the string and the pointer are immutable, ensuring that the parameter cannot be altered within print_string.

Why does both options work in practice? In the example, neither the string nor the pointer is modified in print_string. The relevance of const char * arises when attempting to change the pointed-to string.

Consider the following variations:

• char* the_string: Pointer and value mutable.
• const char* the_string: Value mutable, pointer immutable.
• char* const the_string: Value mutable, pointer immutable.
• const char* const the_string: Value and pointer immutable.

In the provided example, const char * const would be a more appropriate choice to prevent unintended modification of the_string within print_string. It serves as an additional safeguard against potential errors.

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