Converting VOID* to INT ON C/C++

[Jose Diaz]

In the past couple of days i have noticed that a lot of people are having problems casting from one data type to another specially from void to char or int.

First of all void* just means that the variable can pretty much hold any type of data, from character all the way unto float. Let me just show you >>

Lets say you want void *variable;
to be equal 100;

void *variable = 100;

Now this is just going to give you a warning telling you
you did not cast it unto an integer (int).

In order to do that you will do it like this>>

void *variable =(int *) 100;

Now lets work with character(char) >>

char *variable =(char *)"This is a message";

Now am going to show how to do it from a void function unto a int function>>

void *var(void *msg){printf("%s",msg);}

A function call var with an void parameter, Now you
may wonder how do i convert that to an integer(int) function.
Well its very easy >>

char *function=(char *)var("hello world!\n");

First i declare a new variable with data type of int
as pointer then set it equal to an integer function by casting it, then feeding that parameter inside var().


AGAIN!!! That was easy.




I use Dev-C++ 4.9.9.2 if you are having any problems
writing or debugging any program feel free to contact me i will gladly help you. =)

** Edit ** email removed


-JOEY

[donbock]

In C, a void* variable holds a generic data pointer. That is, a void* variable can hold a pointer to any data type. Consider some of the casts recommended by the OP.

void *variable =(int *) 100;

This creates a data pointer with the same bit pattern as the integer "100". The compiler offers no assurance that this pointer can be safely dereferenced.

void *variable =(char *)"This is a message";

I'm surprised this doesn't provoke a compiler error. Perhaps the pointer ends up pointing at this string; perhaps the pointer has the same bit pattern as the first few characters of the string.

void *var(void *msg){printf("%s",msg);}
int *function=(int *)var("hello world!\n");

I'm surprised this doesn't provoke a compiler error. At best, these instructions interconvert data and function pointers. The C Standard explicitly warns that data pointers and function pointers are not guaranteed to be interconvertabl e.

First of all void just means that the variable can pretty much hold any type of data, from character all the way unto float. Let me just show you

This sounds like the Variant type that I've seen in other languages. C definitely does not have a Variant type; I don't know about C++.

[weaknessforcats]

In C++ you cast only because a) you are calling legacy C code that has maybe a void* argument or b) your C++ design is screwed up.

C++ implements various techniques to avoid a typecast.