Void Pointers in C and C : Why Does Casting Matter?

Void Pointers in C and C : Unveiling the Differences

When working with pointers, there are noticeable discrepancies between C and C syntax, particularly in regard to void pointers. In C, the assignment of a void pointer to a pointer of another type is permissible, while in C it requires an explicit cast.

Consider the following example:

<code class="c">int* p = malloc(sizeof(int));</code>

This code compiles successfully in C because malloc returns a void pointer, which can be safely assigned to an integer pointer in C. However, attempting the same in C will result in a compilation error.

However, in a different context, the following code compiles in both C and C without issue:

<code class="c">void foo(void* vptr)
{
}

int main()
{
    int* p = (int*) malloc(sizeof(int));
    foo(p);
    return 0;
}</code>

This discrepancy stems from the implicit and explicit pointer conversions in C and C , respectively. In C, both conversions are implicit, allowing an easy transition between pointer types. However, in C , while conversions from a pointer type to a void pointer remain implicit, conversions in the opposite direction require an explicit cast.

This distinction is highlighted in the C language's reference manual (K&R2), which explicitly states that only conversions from an object pointer to a void pointer are supported without information loss.

In comparison, the C standard dictates more stringent rules, mandating an explicit cast when converting from a void pointer to any other pointer type, thus ensuring type safety and preventing potential pointer errors.

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