Interpreting Complex C Declarations


Once you start mixing pointers to functions in your C declarations you’ll notice that things can get complex. For example, what does the following declaration represent:

float * (* (*ptr)(int))(double **,char c)

What about this one:

unsigned **( * (*ptr) [5] ) (char const *,int *)

One tool you can use to help you with those complex declarations is called cdecl.org. You can type the C declaration and the tool will translate it into English to you, and vice-versa.

This tool also comes with GCC, so you can use it via the command line as well.

And here are is what the above declarations stand for:

First one: ptr is a pointer to a function that takes as parameter an int, and returns a pointer to a function that takes as parameters a pointer to pointer to double and a char, and returns a pointer to float.

Second one: ptr is a pointer to an array of five pointers to functions that take as parameters a constant pointer to char and a pointer to int, returning a pointer to a pointer of unsigned int.

There was a question about those declarations a while ago on Programmers.StackExchange.com.

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