Alternative to typedef?

Hey everyone, I have a problem. This is what I'm trying to do (but a lot simplified):

Code:

---

int a;
//stuff
void myFunction()
{
    if(a == 1)
          typedef char data_type;
    else if(a == 2)
          typedef short data_type;
    else
          typedef long data_type;
}

void function2()
{
    data_type* x = (data_type*)myData; //myData is a void*
    //do stuff with x
}

---

that's the basic idea of what I want to do, but this won't work since typedef can't be used inside a function's definition. Is there any alternative way to achieve the same purpose? (function2 is always called after myFunction) :confused:

typedefs DO work in functions.

Really? But off the MSDN library on my comp, it says:

Quote:

---

You cannot use the typedef specifier inside a function definition.

---

Is there some hidden meaning I'm missing?

if you declare a typedef inside a function it's going to only be local to that function

EDIT: also, since your typedef's are in the if blocks, they are only valid from WITHIN those if blocks. Besides, typedefs are compile-time, not runtime, which is a point that I think you are missing.

oh... I see. But is there any way to achieve a similar effect with what I intended to happen actually happening? (i.e. so I won't have to do the if/else-ing in function2, which gets called several hundred times more frequently than myFunction does :eek: )

**EDIT**
Well, actually the function names are:
myFunction() = lock()
function2() = setPixel()

depends, is the variable 'a' going to vary at runtime?

EDIT: Seems to me like you want templating anyways. If not, if a never changes at runtime, you can use #define, but I don't recommend that.

Well, maybe but not too much: a = the bpp of a ddraw surface

then make the funtion templated and put the function2() calls in the if/elses blocks of the function that CALLS function2()

Hmm, I don't really follow you. What do you mean by templated?

don't mean to be rude, but maybe you should learn C++ before you toy with DirectX.

>typedefs DO work in functions.
Not according to the standard:

Code:

---

7.1.3 The typedef specifier

Declarations containing the decl-specifier typedef declare identifiers that can be used later for naming
fundamental (3.9.1) or compound (3.9.2) types. The typedef specifier shall not be used in a function-
definition (8.4), and it shall not be combined in a decl-specifier-seq with any other kind of specifier
except a typespecifier.

---

-Prelude

Quote:

---

Originally posted by Prelude
>typedefs DO work in functions.
Not according to the standard:

Code:

---

7.1.3 The typedef specifier

Declarations containing the decl-specifier typedef declare identifiers that can be used later for naming
fundamental (3.9.1) or compound (3.9.2) types. The typedef specifier shall not be used in a function-
definition (8.4), and it shall not be combined in a decl-specifier-seq with any other kind of specifier
except a typespecifier.

---

-Prelude

---

*Runs home crying*

I guess that's just another folly of msvc++ then. It compiles fine and works "properly" over here.

Maybe I should learn C++ then :p

:) I have learned c++, or at least enough to get by. And the question I just asked is not a matter of DirectX-work-or-not-work, but a matter of convenience and maybe performance... I guess if this is too advanced for me (*sniff*) I'll just skip this bit :(

Quote:

---

typedef's are compile-time and not run-time

---

Yeah, I sort of figured that out after some experimentation... well, I wasn't sure but it really looked like it, based on compiler behaviour.

Code:

---

int a;
void* myData;

template<class data_type>
void function2()
{
    data_type* x = (data_type*)myData;
}

void myFunction()
{
    if(a == 1)
        function2<char>();
    else if(a == 2)
        function2<short>();
    else
        function2<long>();
}

---

Ah, I see. That would be a great help :) But, unfortunately, myFunction() isn't supposed to call function2(). Would this work instead?

Code:

---

int a;
void* myData;
void (*pFunction2) ();

template<class data_type>
void function2()
{
    data_type* x = (data_type*)myData;
}

void myFunction()
{
    if(a == 1)
        pfunction2 = function2<char>;
    else if(a == 2)
        pfunction2 = function2<short>;
    else
        pfunction2 = function2<long>;
}

---

yup

Ok, thanks alot! :)

**EDIT**

P.S.
Function pointers don't slow things down any, do they?

>Function pointers don't slow things down any, do they?
Not enough to worry about.

-Prelude

Ok, that's good. But another thing just occured to me - Templates don't slow things down either, do they? :D

Nope templates are 100% compile time. It's as fast as if you just manually redid the function. Each different version of the templated function is a completely different function.

Ok, sounds great. Thanks alot everyone! (I'll be sure to pester you guys with more questions if I run into trouble :D)