Thread: Assigning void* to a variable

I am working on a testing tool called RTRT. There is a line of testing as,

FORMAT buffer = void*

what happens after the above line is executed. Will buffer variable be used to point to the start of a particular size of memory? if yes, what will be the size of the memory?

Originally Posted by boonflies

I am working on a testing tool called RTRT. There is a line of testing as,

FORMAT buffer = void*

what happens after the above line is executed. Will buffer variable be used to point to the start of a particular size of memory? if yes, what will be the size of the memory?

I don't know what "RTRT" is, or what "FORMAT" is.

A "void *" is a generic pointer that can be assigned to any pointer type. For example, malloc() returns a void *.

Code:

// ...
char *ptr = NULL;
ptr = malloc(256);
// ....

In previous C Standards malloc() would return a "char *" that would need to be cast to the type of the pointer being assigned. It is also used in functions like qsort()

@jack jordan

I try to steer away from void pointers

Don't "steer clear" of them! Learn what they are and how to use them properly!

In understanding void*, I have my own curiosity. From the OP's code, it isn't clear what the line of code is doing because FORMAT is not known, but what can be assumed? I think

Code:

FORMAT buffer

is an lvalue and

Code:

void*

is supposed to be an rvalue. However, I do not believe void* in itself can be an rvalue. At least in my IDE, it highlights it as an error. I think in order for void* to be an rvalue, it needs to call something that returns a value much like malloc. I think I had assumed that void* could just be assigned to a pointer to make it deliberately point to nothing rather than a random something. Because of this, I was a little confused as to what value it might have over NULL. I don't believe this is the case now as I can't find any examples of code such as

Code:

int ptr = void*;

I guess I am now assuming these examples do not exist, and this kind of code is a syntax error.

The OP's code is not legal C code. It is part of "Rational Test Realtime", an IBM product.

As for "void *". This is a C data type, not an rvalue or lvalue.

Code:

int x = 10;
int y = 0;

// In the following statement, x is an rvalue, the value stored in x, or the integer 10.
// y is an lvalue, or basically the location where to store the rvalue, 10.

y = x;

// Now the integer y is equal to the integer x.
// lvalues MUST be a variable that can be assigned.
// rvalues can be variables, constants, MACROS, a math expression, or the return value from a function call.

malloc() does return a "void *" rvalue, and can be assigned to an lvalue object, as I shown in my previous post.

You need to go back and study pointers as defined in C99 and C11 C Programming Standards.