What do the parentheseses mean in the c code? [duplicate]

I'm not even a beginner of c language.

and I see the codes from cpython source code:

typedef struct _formatdef {
    char format;
    Py_ssize_t size;
    Py_ssize_t alignment;
    PyObject* (*unpack)(_structmodulestate *, const char *,
                        const struct _formatdef *);
    int (*pack)(_structmodulestate *, char *, PyObject *,
                const struct _formatdef *);
} formatdef;

in the 5th line, I know that PyObject* is defining a pointer to a variable of PyObject type, however what does (*unpack) mean? and what does the following (_structmodulestate *) mean?

It's a function pointer declaration.

This:

float x;

declares a variable of type float named x.

This:

float *p;

declares a variable of type float* (a pointer to a float) named p.

This:

int foo(float *p);

declares a function named foo, which takes a float* as an argument, and returns an int.

This:

PyObject* (*unpack)(_structmodulestate *, const char *, const struct _formatdef *);

declares a function pointer named unpack, which points to a function which takes three pointers (of various types) as arguments, and returns a PyObject*.