Communities

Writing
Writing
Codidact Meta
Codidact Meta
The Great Outdoors
The Great Outdoors
Photography & Video
Photography & Video
Scientific Speculation
Scientific Speculation
Cooking
Cooking
Electrical Engineering
Electrical Engineering
Judaism
Judaism
Languages & Linguistics
Languages & Linguistics
Software Development
Software Development
Mathematics
Mathematics
Christianity
Christianity
Code Golf
Code Golf
Music
Music
Physics
Physics
Linux Systems
Linux Systems
Power Users
Power Users
Tabletop RPGs
Tabletop RPGs
Community Proposals
Community Proposals
tag:snake search within a tag
answers:0 unanswered questions
user:xxxx search by author id
score:0.5 posts with 0.5+ score
"snake oil" exact phrase
votes:4 posts with 4+ votes
created:<1w created < 1 week ago
post_type:xxxx type of post
Search help
Notifications
Mark all as read See all your notifications »
Q&A

Welcome to Software Development on Codidact!

Will you help us build our independent community of developers helping developers? We're small and trying to grow. We welcome questions about all aspects of software development, from design to code to QA and more. Got questions? Got answers? Got code you'd like someone to review? Please join us.

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

Parent

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

+5
−1

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?
}
History
Why does this post require moderator attention?
You might want to add some details to your flag.
Why should this post be closed?

1 comment thread

Decoding C declarations (1 comment)
Post
+6
−1

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 an arbitrary number of 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). 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.

History
Why does this post require moderator attention?
You might want to add some details to your flag.

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)
Probably worth noting...
Canina‭ wrote over 2 years ago

It's probably worth noting that as used here, function pointers don't really bring any benefit and do introduce potentially significant complexity; but there are some tasks that are made significantly easier by using them. As one example of the latter, consider something like a dynamic switch() which is very difficult (dare I say impossible?) to do without function pointers, but becomes an almost trivial (not quite, because function pointers are never trivial) exercise with function pointers.