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Q&A

What does a variable followed by parentheses ("ptr()") mean?

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−0

What does ptr() mean in this code?

#include<stdio.h>
#include<stdlib.h>

void PrintHello()
{
    printf("Hello\n"); 
}

int Add(int a, int b)
{
    return a+b;
}

int main ()
{
    void (*ptr)();
    ptr = PrintHello;
    ptr(); //For this specific line of code, what does it mean?
}
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1 comment thread

Decoding C declarations (1 comment)

1 answer

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void (*ptr)() defines a function pointer. It says that ptr is a pointer to a function. But that function must have a void return type, and take no parameters (that's what the empty parentheses defines).

Then, ptr = PrintHello assigns the PrintHello function to the ptr pointer (and it works because PrintHello matches the signature: it has a void return type and takes no parameters). So, now ptr is pointing to PrintHello.

Finally, ptr() is calling the function that ptr points to (in this case, PrintHello). It has the same effect as calling PrintHello(), and the parentheses are needed because it's a function call. But the function takes no parameters, thus the empty parentheses.

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2 comment threads

Empty parentheses mean "any number of parameters" (this feature is not very useful, and can lead to s... (1 comment)
Probably worth noting... (1 comment)

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