const char * const vs const char *: When to Use Which?

const char * const versus const char *

In C , when dealing with pointers and constants, it is crucial to understand the distinction between const char * const and const char *.

Function Parameter Declaration

Consider the following example function:

<code class="cpp">void print_string(const char * the_string);</code>

This type of declaration states that the_string is a pointer to a character (i.e., char *), but the content pointed to by the_string is constant (i.e., const char). This means that you cannot modify the characters in the string.

Alternative Declaration: const char * const

Using const char * const instead of const char * adds an additional level of protection. It states that the_string itself is a constant pointer. This prevents you from modifying the_string inside the print_string function.

When to Use Which?

const char * (pointer to a constant character): Use this when you need to pass a pointer to a string that should not be modified, but you may need to change the pointer itself. For example, when iterating through an array of strings.

const char * const (constant pointer to a constant character): Use this when you want to ensure that neither the pointer nor the content it points to can be modified. This is often used for protecting critical data structures or ensuring consistency.

In the case of the example code provided:

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

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

Using const char * const would be more appropriate as it would prevent any accidental modifications to the string inside the print_string function. However, the choice depends on the intended usage and whether or not the pointer needs to be reassigned later.

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