Is it possible to dereference the void pointer without type-casting in C programming language...
No, void
indicates the absence of type, it is not something you can dereference or assign to.
is there is any way of generalizing a function which can receive pointer and store it in void pointer and by using that void pointer we can make a generalized function..
You cannot just dereference it in a portable way, as it may not be properly aligned. It may be an issue on some architectures like ARM, where pointer to a data type must be aligned at boundary of the size of data type (e.g. pointer to 32-bit integer must be aligned at 4-byte boundary to be dereferenced).
For example, reading uint16_t
from void*
:
/* may receive wrong value if ptr is not 2-byte aligned */
uint16_t value = *(uint16_t*)ptr;
/* portable way of reading a little-endian value */
uint16_t value = *(uint8_t*)ptr
| ((*((uint8_t*)ptr+1))<<8);
Also, is pointer arithmetic with void pointers possible...
Pointer arithmetic is not possible on pointers of void
due to lack of concrete value underneath the pointer and hence the size.
void* p = ...
void *p2 = p + 1; /* what exactly is the size of void?? */
Function pointers in C
Let's start with a basic function which we will be pointing to:
int addInt(int n, int m) {
return n+m;
}
First thing, let's define a pointer to a function which receives 2 int
s and returns an int
:
int (*functionPtr)(int,int);
Now we can safely point to our function:
functionPtr = &addInt;
Now that we have a pointer to the function, let's use it:
int sum = (*functionPtr)(2, 3); // sum == 5
Passing the pointer to another function is basically the same:
int add2to3(int (*functionPtr)(int, int)) {
return (*functionPtr)(2, 3);
}
We can use function pointers in return values as well (try to keep up, it gets messy):
// this is a function called functionFactory which receives parameter n
// and returns a pointer to another function which receives two ints
// and it returns another int
int (*functionFactory(int n))(int, int) {
printf("Got parameter %d", n);
int (*functionPtr)(int,int) = &addInt;
return functionPtr;
}
But it's much nicer to use a typedef
:
typedef int (*myFuncDef)(int, int);
// note that the typedef name is indeed myFuncDef
myFuncDef functionFactory(int n) {
printf("Got parameter %d", n);
myFuncDef functionPtr = &addInt;
return functionPtr;
}
Best Answer
No this is not legal. A
void*
cannot be arbitrarily incremented. It needs to be cast to a specific type first.If you want to increment it by a specific number of bytes then this is the solution I use.
The
char
type is convenient because it has a defined size of 1 byte.EDIT
It's interesting that it runs on gcc with a warning. I tested on Visual Studio 2010 and verified it does not compile. My limited understanding of the standard would say that gcc in the error here. Can you add the following compilation flags