explanation of this complex typedef [duplicate]

Question

so what does this typedef syntax actually do?

typedef PIMAGE_NT_HEADERS (WINAPI *CHECKSUMMAPPEDFILE)
          (PVOID baseAddress, DWORD fileLength, PDWORD headerSum, PDWORD checkSum);

from what I know typedef is used like this typedef oldtype newtype; but overhere the whole thing looks like a prototype of a function, but it also looks like it is creating a new type of PIMAGE_NT_HEADERS...

as somebody responded "function typedefs" but an example of a function typedef can bye this

typedef int multiply(int arg1, int arg2);

where multiply is the function name, but in the complex one I posted above, where is the function name?

I've just edited your question to put a linebreak in the declaration, so we can see it without needing to scroll. Feel free to revert if you don't like it. — Martin Bonner supports Monica
– Martin Bonner supports Monica, Commented Aug 26, 2016 at 11:31

Community · Accepted Answer · 2017-05-23 12:22:50Z

2

Your typedef creates an alias CHECKSUMMAPPEDFILE. CHECKSUMMAPPEDFILE is a pointer to a function that returns an PIMAGE_NT_HEADERS and takes as arguments PVOID baseAddress, DWORD fileLength, PDWORD headerSum, PDWORD checkSum. From the first look syntax of such a typedef is not obvious.

and WINAPI is calling convention.

edited May 23, 2017 at 12:22

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answered Aug 26, 2016 at 10:54

Nikita

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2 Comments

IInspectable Over a year ago

... and uses the WINAPI calling convention.

Nikita Over a year ago

@IInspectable Missed it, thnx!

marcinj · Accepted Answer · 2016-08-26 11:34:50Z

This is a type alias for a function pointer. You can use it to define a variable to which you can assign a function.

This:

typedef int multiply(int arg1, int arg2);

is a typedef for a function type, you cannot use it the same way as function pointer. See example below:

int mul(int arg1, int arg2) {
}

typedef int multiply(int arg1, int arg2);
int main() {
    //multiply m = mul; // error multiply is a typedef for a funciton type
    multiply* m = mul; // ok
}

What your type alias :

typedef PIMAGE_NT_HEADERS (WINAPI *CHECKSUMMAPPEDFILE)(PVOID baseAddress,   
                               DWORD fileLength, PDWORD headerSum, PDWORD checkSum);

do:

it declares a CHECKSUMMAPPEDFILE as pointer to function (PVOID, DWORD, PDWORD, PDWORD) with WINAPI calling convention returning PIMAGE_NT_HEADERS

You might use cdecl.org to decifer function pointers, it offen requires some tweaking to make it work.

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