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Why is this ALWAYS happening to me!?
June 09, 2002 10:00 AM
I need help. I have this function which uses structures.
The thing is, it can use all kinds of structures:
struct Foo
{
int a,b,c,d;
};
struct Bar
{
int e,f,g,h;
};
struct myStruct
{
int I,feel,good;
};
the structure has a parameter where i insert a pointer of a structure which i then can use to poke around in a memory "pool" of which the structure creates.
UnknownFunction(0,0,(BYTE**)&structFoo);
structFoo[0].a = 1211;
structFoo[0].b = 2422;
structFoo[0].c = 3633;
UnknownFunction(0,0,(BYTE**)&structBar);
structBar[0].e = 1211;
structBar[0].f = 2422;
structBar[0].g = 3633;
UnknownFunction(0,0,(BYTE**)&myStruct);
myStruct[0].I = 1;
myStruct[0].feel = 1;
myStruct[0].good = 0;
Now I *_really_* hate defining pointers which I''m only going to use once, so i''ve made my own function of which stores a structure i provide, in a predefined pointer.
I.e:
void *pStruct;
which I SHOULD be able to use: pStruct.x = dumdedum;
But when I do this, the program keeps complaining about "Size unknown!!". Is it even POSSIBLE to have a pointer which can change in type? Or something like that?
I.e:
MyFunc(Foo); //pStruct = Foo;
pStruct[0].a = 0; //instead of Foo[0].a = 0
MyFunc(Bar); //pStruct = Bar;
pStruct[0].e = 0; //instead of Bar[0].e = 0
MyFunc(myStruct); //pStruct = myStruct;
pStruct[0].Good = 0; //instead of myStruct[0].Good = 0
Js
123
June 09, 2002 10:19 AM
quote:
Original post by the_recon
I need help. I have this function which uses structures.
The thing is, it can use all kinds of structures:
struct Foo
{
int a,b,c,d;
};
struct Bar
{
int e,f,g,h;
};
struct myStruct
{
int I,feel,good;
};
the structure has a parameter where i insert a pointer of a structure which i then can use to poke around in a memory "pool" of which the structure creates.
What do you mean with "the structure has a parameter"?? Structures
doesn''t have parameters. Do you mean member?
quote:
UnknownFunction(0,0,(BYTE**)&structFoo);
structFoo[0].a = 1211;
structFoo[0].b = 2422;
structFoo[0].c = 3633;
UnknownFunction(0,0,(BYTE**)&structBar);
structBar[0].e = 1211;
structBar[0].f = 2422;
structBar[0].g = 3633;
UnknownFunction(0,0,(BYTE**)&myStruct);
myStruct[0].I = 1;
myStruct[0].feel = 1;
myStruct[0].good = 0;
Now I *_really_* hate defining pointers which I''m only going to use once, so i''ve made my own function of which stores a structure i provide, in a predefined pointer.
I.e:
void *pStruct;
which I SHOULD be able to use: pStruct.x = dumdedum;
No. The compiler needs to know the size of the structure so you
can use the brackets, and .x... There''s no way for the compiler to
know which type of structure it is. There can be many different
types of structures which have a "x" member
quote:
But when I do this, the program keeps complaining about "Size unknown!!". Is it even POSSIBLE to have a pointer which can change in type? Or something like that?
I.e:
MyFunc(Foo); //pStruct = Foo;
pStruct[0].a = 0; //instead of Foo[0].a = 0
MyFunc(Bar); //pStruct = Bar;
pStruct[0].e = 0; //instead of Bar[0].e = 0
MyFunc(myStruct); //pStruct = myStruct;
pStruct[0].Good = 0; //instead of myStruct[0].Good = 0
MyFunc(Foo); //pStruct = Foo;
((Foo*)pStruct)[0].a = 0; //instead of Foo[0].a = 0
MyFunc(Bar); //pStruct = Bar;
((Bar*)pStruct)[0].e = 0; //instead of Bar[0].e = 0
MyFunc(myStruct); //pStruct = myStruct;
((myStruct*)pStruct)[0].Good = 0; //instead of myStruct[0].Good = 0
Joakim Asplund
http://megajocke.cjb.net
Joakim Asplundhttp://megajocke.y2.org
372
June 10, 2002 09:27 AM
What you are trying to do is quite dangerous and even if it is possible, you shouldn''t do it anyway. Go back to your drawing board and find another way to do whatever it is you''re trying to do.
If you''re intent on playing around with memory, I recommend learning C++. At least then you could do your poking around in a type-safe fashion
**''s and C type casts send uneasy shivers down my spine every time I see them and the bad memories come back...
Besides, if --I-- was going to poke around memory (which I might add is bad practise) then I would first of all create an alias:
typedef void* LPVOIDPTR;
Then all I would do is typecast the structure to a pure pointer and read in the data as a sequential stream of bytes.
Just dont bother, k?
-------- E y e .Scream Software --------
----------------------------------------
/-\
http://www.eyescream.cjb.net | * |
\-/
----------------------------------------
If you''re intent on playing around with memory, I recommend learning C++. At least then you could do your poking around in a type-safe fashion
**''s and C type casts send uneasy shivers down my spine every time I see them and the bad memories come back...Besides, if --I-- was going to poke around memory (which I might add is bad practise) then I would first of all create an alias:
typedef void* LPVOIDPTR;
Then all I would do is typecast the structure to a pure pointer and read in the data as a sequential stream of bytes.
Just dont bother, k?
-------- E y e .Scream Software --------
----------------------------------------
/-\
http://www.eyescream.cjb.net | * |
\-/
----------------------------------------
122
June 10, 2002 04:46 PM
struct eins
{
int i;
...
} x;
struct zwei
{
int j;
...
} y;
void * p;
p = &x
cout << (struct eins *)(p)->i;
p = &y
cout << (struct zwei *)(p)->j; // These 2 lines are
cout << (struct eins *)(p)->i; // identical.
The last thing will only work when your structures have the same variable type at the same offset. Dont do such things unless youre absolutly sure it will make things easier.
-> x.i == (struct zwei *)(&x)->j;
Maybe you can use a union.
However, as was already pointed out, the compiler has no way to know what structure you mean if you dont tell him (unlike perl).
[edited by - Ketzer on June 10, 2002 5:48:15 PM]
{
int i;
...
} x;
struct zwei
{
int j;
...
} y;
void * p;
p = &x
cout << (struct eins *)(p)->i;
p = &y
cout << (struct zwei *)(p)->j; // These 2 lines are
cout << (struct eins *)(p)->i; // identical.
The last thing will only work when your structures have the same variable type at the same offset. Dont do such things unless youre absolutly sure it will make things easier.
-> x.i == (struct zwei *)(&x)->j;
Maybe you can use a union.
However, as was already pointed out, the compiler has no way to know what structure you mean if you dont tell him (unlike perl).
[edited by - Ketzer on June 10, 2002 5:48:15 PM]
June 11, 2002 03:41 PM
Are you using C or C++? If you are using C++ you might not be able to do that at all(don''t quote me)...
Why don''t you use void *?
Why don''t you use void *?
929
June 11, 2002 05:11 PM
Templates anyone?
Death of one is a tragedy, death of a million is just a statistic.
Death of one is a tragedy, death of a million is just a statistic.
If at first you don't succeed, redefine success.
122
June 12, 2002 06:27 AM
The only thing that wont work in C is the cout, apart from that there should be no problems.
As for templates .. that is one part of c i have no clue about.
As for templates .. that is one part of c i have no clue about.
523
June 12, 2002 07:46 AM
If you are willing to use C++, this will give you the functionality you want.
Here is another option, depending on what you are looking for:
ps. Both these samples work, I compiled and ran them.
[EDIT] You can do the same thing with structs, but you cannot directly access the members with inheritance in this fashion, because you have to use the virtual keyword and that only works on methods(I think).
---
Make it work.
Make it fast.
"Commmmpuuuuterrrr.." --Scotty Star Trek IV:The Voyage Home
[edited by - CaptainJester on June 12, 2002 8:49:57 AM]
#include <iostream>class BaseClass {public: BaseClass() {x=0;y=0;} virtual void setX(int a) {x=a;} virtual void setY(int b) {y=b;} virtual int getX() {return x;} virtual int getY() {return y;}private: int x,y;};class FooClass:public BaseClass {public: FooClass() {x=1;y=1;} void setX(int a) {x=a;} void setY(int b) {y=b;} int getX() {return x;} int getY() {return y;}private: int x,y;};class BarClass:public BaseClass {public: BarClass() {x=2;y=2;} void setX(int a) {x=a;} void setY(int b) {y=b;} int getX() {return x;} int getY() {return y;}private: int x,y;};void UnknownFunction(int a,int b,BaseClass *test) { test->setX(a); test->setY(b);}int main(int argc, char *argv[]) { BaseClass *base=new BaseClass(); FooClass *foo=new FooClass(); BarClass *bar=new BarClass(); cout << "base->x=" << base->getX() << endl; cout << "base->y=" << base->getY() << endl; cout << "foo->x=" << foo->getX() << endl; cout << "foo->y=" << foo->getY() << endl; cout << "bar->x=" << bar->getX() << endl; cout << "bar->y=" << bar->getY() << endl; UnknownFunction(3,4,base); UnknownFunction(5,6,foo); UnknownFunction(7,8,bar); cout << "base->x=" << base->getX() << endl; cout << "base->y=" << base->getY() << endl; cout << "foo->x=" << foo->getX() << endl; cout << "foo->y=" << foo->getY() << endl; cout << "bar->x=" << bar->getX() << endl; cout << "bar->y=" << bar->getY() << endl; return 0;} Here is another option, depending on what you are looking for:
#include <iostream>class BaseClass {public: BaseClass() {x=0;y=0;} virtual void setX(int a) {x=a;} virtual void setY(int b) {y=b;} virtual int getX() {return x;} virtual int getY() {return y;}protected: int x,y;};class FooClass:public BaseClass {public: FooClass() {x=1;y=1;} void setX(int a) {x=a;} void setY(int b) {y=b;} int getX() {return x;} int getY() {return y;}};class BarClass:public BaseClass {public: BarClass() {x=2;y=2;} void setX(int a) {x=a;} void setY(int b) {y=b;} int getX() {return x;} int getY() {return y;}};void UnknownFunction(int a,int b,BaseClass *test) { test->setX(a); test->setY(b);}int main(int argc, char *argv[]) { BaseClass *base=new BaseClass(); FooClass *foo=new FooClass(); BarClass *bar=new BarClass(); cout << "base->x=" << base->getX() << endl; cout << "base->y=" << base->getY() << endl; cout << "foo->x=" << foo->getX() << endl; cout << "foo->y=" << foo->getY() << endl; cout << "bar->x=" << bar->getX() << endl; cout << "bar->y=" << bar->getY() << endl; UnknownFunction(3,4,base); UnknownFunction(5,6,foo); UnknownFunction(7,8,bar); cout << "base->x=" << base->getX() << endl; cout << "base->y=" << base->getY() << endl; cout << "foo->x=" << foo->getX() << endl; cout << "foo->y=" << foo->getY() << endl; cout << "bar->x=" << bar->getX() << endl; cout << "bar->y=" << bar->getY() << endl; return 0;} ps. Both these samples work, I compiled and ran them.
[EDIT] You can do the same thing with structs, but you cannot directly access the members with inheritance in this fashion, because you have to use the virtual keyword and that only works on methods(I think).
---
Make it work.
Make it fast.
"Commmmpuuuuterrrr.." --Scotty Star Trek IV:The Voyage Home
[edited by - CaptainJester on June 12, 2002 8:49:57 AM]
"None of us learn in a vacuum; we all stand on the shoulders of giants such as Wirth and Knuth and thousands of others. Lend your shoulders to building the future!" - Michael Abrash[JavaGaming.org][The Java Tutorial][Slick][LWJGL][LWJGL Tutorials for NeHe][LWJGL Wiki][jMonkey Engine]
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