What's the purpose of declaring function as pointers?

Hi Mentors,

I am bit confused as why does one need to declared the functions as pointers.

For example I was going through fgets functions which has the following prototype defined in stdio.h

char *fgets(char *str, int size, FILE* file);

Please provide your valuable inputs.

Thanks
Ankit

That's not an example of a function pointer. What 'fgets' does is return a char pointer.

For starters, the arguments of fgets() aren't function pointers. Look at the signal() syscall for an example of function pointers and it'll also tell you why 'n where they are applicable.

Quote:

---

Originally Posted by nonoob

That's not an example of a function pointer. What 'fgets' does is return a char pointer.

---

but what does char *fgets () mean ?

means fgets returns a string.
You can do

Code:

---

char *pnt;
...
pnt = fgetc(buffer, 100, stream); /* returns a string */
printf("String is %s\n", pnt);

---

I'm not sure why one would want to look at that string if the buffer variable is designed to contain it. But there are times when the returned pointer is NULL - some error occurred.

Quote:

---

Originally Posted by nonoob

means fgets returns a string.

---

No, it means that fgets() returns a pointer to char.

A string is something different from a pointer. By convention, however, if fgets() returns non-NULL, the data at that address is a collection of contiguous char's, with the last one zero (which is how strings are represented in the C standard library).

fgets() returns a NULL pointer if an error occurs or, if no characters have been read, the end of the stream has been reached.

Quote:

---

Originally Posted by ankiit

I am bit confused as why does one need to declared the functions as pointers.

---

A function can't really be declared as a pointer, but you can declare a pointer to a function. That would be a "function pointer", but as a few people have said, this isn't one.

All functions have a type; it may be any type, but it must be the same type as the value returned by the function. If the function does not return anything, its type should be void. Note that this is not the same as void*; a void function returns nothing, but a void* function returns a pointer to a void type.

The type of fgets() is char*, because fgets returns a pointer to a char type.

A char pointer may point to the beginning of a string. In practice, it almost always is.

Hi ,

I know some information about that function pointer that we can use them more in callback functions.

Quote:

---

Originally Posted by nkrao123@gmail.

Hi ,

I know some information about that function pointer that we can use them more in callback functions.

---

Where did you see function pointers here ?