Easy questions about C++ [modified]
-
Hi guys, I'm using Visual Studio 2005 and I have few questions: 1. If I have function without parameters, what to do to skip () when invoking the function? 2. I have:
int Mem;
...
Mem = LocalAlloc(LHND, ...);
...
WriteFile(f, Mem,...)Mem keeps address of memory block. What expression to write in WriteFile(f, ???Mem,...) to write the memory block pointed by Mem in file? 3. Is there a way a class member field to be accessible just for reading without writing? P.S. If you know the answer of at least 1 question, please share it.
modified on Friday, November 21, 2008 6:29 AM
-
Hi guys, I'm using Visual Studio 2005 and I have few questions: 1. If I have function without parameters, what to do to skip () when invoking the function? 2. I have:
int Mem;
...
Mem = LocalAlloc(LHND, ...);
...
WriteFile(f, Mem,...)Mem keeps address of memory block. What expression to write in WriteFile(f, ???Mem,...) to write the memory block pointed by Mem in file? 3. Is there a way a class member field to be accessible just for reading without writing? P.S. If you know the answer of at least 1 question, please share it.
modified on Friday, November 21, 2008 6:29 AM
akirilov wrote:
1. If I have function without parameters, what to do to skip () when invoking the function?
You can't. Why do you want to do such a thing ?
akirilov wrote:
int Mem; - it keep address of memory block.
Why are you working with integers to store addresses ? Why not manipulate pointers directly, it will make your life much easier.
akirilov wrote:
3. Is there a way a class member field to be accessible just for reading without writing?
Make it private and provide a getter method and no setter method in the class.
Cédric Moonen Software developer
Charting control [v1.5] OpenGL game tutorial in C++ -
Hi guys, I'm using Visual Studio 2005 and I have few questions: 1. If I have function without parameters, what to do to skip () when invoking the function? 2. I have:
int Mem;
...
Mem = LocalAlloc(LHND, ...);
...
WriteFile(f, Mem,...)Mem keeps address of memory block. What expression to write in WriteFile(f, ???Mem,...) to write the memory block pointed by Mem in file? 3. Is there a way a class member field to be accessible just for reading without writing? P.S. If you know the answer of at least 1 question, please share it.
modified on Friday, November 21, 2008 6:29 AM
1. As far as i know there's no standard way to do that. 2. What do you mean? If you want the address of the Mem variable, then use &, so &Mem. If you store a memory location in Mem, then use a pointer type, like int *Mem, but if you want to convert int to a pointer, then you can use for example (void *)Mem. 3. You can declare const "variables" to which you specify a value and then it cannot be modified anymore. For example const int m_Constant;, you would give a value to this in the contstructor of yor class. If you want to modify a variable "inside" the containing class but not outside then declare it as protected or private amd supply either a Get method for it or a const reference to it. so if you have int m_variable; then you can do either const int &GetVariable() { return m_variable; } or you can do const int &m_constVariable; and initialize this in the constructor using m_variable.
-
akirilov wrote:
1. If I have function without parameters, what to do to skip () when invoking the function?
You can't. Why do you want to do such a thing ?
akirilov wrote:
int Mem; - it keep address of memory block.
Why are you working with integers to store addresses ? Why not manipulate pointers directly, it will make your life much easier.
akirilov wrote:
3. Is there a way a class member field to be accessible just for reading without writing?
Make it private and provide a getter method and no setter method in the class.
Cédric Moonen Software developer
Charting control [v1.5] OpenGL game tutorial in C++Make it private and provide a getter method and no setter method in the class.Invoking methods is slow. Is there any other way (Something like in Delphi - you can give read/write access to a member, without involving methods)?Why not manipulate pointers directly, it will make your life much easier.Mainly, because I'don't know how :) and also I had problems with pointer arithmetics. Anyway could you share a code fragment that will do the trick (with pointers) (if possible with int)? -
1. As far as i know there's no standard way to do that. 2. What do you mean? If you want the address of the Mem variable, then use &, so &Mem. If you store a memory location in Mem, then use a pointer type, like int *Mem, but if you want to convert int to a pointer, then you can use for example (void *)Mem. 3. You can declare const "variables" to which you specify a value and then it cannot be modified anymore. For example const int m_Constant;, you would give a value to this in the contstructor of yor class. If you want to modify a variable "inside" the containing class but not outside then declare it as protected or private amd supply either a Get method for it or a const reference to it. so if you have int m_variable; then you can do either const int &GetVariable() { return m_variable; } or you can do const int &m_constVariable; and initialize this in the constructor using m_variable.
2. With some code will be easier to explain:
int Mem;
...
Mem = LocalAlloc(LHND, ...);
...
WriteFile(f, (void *) Mem,...)I receive exception during runtime, so my question is what expression to use so it will work properly (writes the pointed by Mem block to file)
-
2. With some code will be easier to explain:
int Mem;
...
Mem = LocalAlloc(LHND, ...);
...
WriteFile(f, (void *) Mem,...)I receive exception during runtime, so my question is what expression to use so it will work properly (writes the pointed by Mem block to file)
Ok, new edit, i misread you there the first time. LocalAlloc gives you a handle to a memory location, not the memory location itself. Declare your variable as HANDLE, not int, since LocalALloc, unless specified differently, will give you a HANDLE. You have to use LocalLock and LocalUnlock to actually access the memory. But may i ask why you need to use LocalAlloc instead of new or malloc? So basicly, if you have to use LocalAlloc you have to LocalLock(handle), this will give you a void * pointer that points at the memory you allocated, you can feed this to WriteFile (didn't go into WriteFile itself so i assume you know what you are doing with that) and then use LocalUnlock to unlock the memory, also use LocalFree to free it.
modified on Friday, November 21, 2008 6:36 AM
-
Make it private and provide a getter method and no setter method in the class.Invoking methods is slow. Is there any other way (Something like in Delphi - you can give read/write access to a member, without involving methods)?Why not manipulate pointers directly, it will make your life much easier.Mainly, because I'don't know how :) and also I had problems with pointer arithmetics. Anyway could you share a code fragment that will do the trick (with pointers) (if possible with int)?akirilov wrote:
Invoking methods is slow
no; using inline might help a little bit, and probably the compiler will optimize this also.
akirilov wrote:
because I'don't know how
what a good occasion to learn.
This signature was proudly tested on animals.
-
Make it private and provide a getter method and no setter method in the class.Invoking methods is slow. Is there any other way (Something like in Delphi - you can give read/write access to a member, without involving methods)?Why not manipulate pointers directly, it will make your life much easier.Mainly, because I'don't know how :) and also I had problems with pointer arithmetics. Anyway could you share a code fragment that will do the trick (with pointers) (if possible with int)?akirilov wrote:
Invoking methods is slow.
As a famous guy already said: "Premature optimization is the root of all evil". What it means here is that you try to have only optimization in mind even when it makes your code less readable or maintainable. Unless your function has to be called very often and is in a time critical part of your code, I think you can forget about the performances (and you can also rely on your compiler for a bit of optimizations). If I take your way of thinking to the extreme, you can end up with one gigantic main function because you never wanted to make function calls...
akirilov wrote:
Anyway could you share a code fragment that will do the trick (with pointers) (if possible with int)?
I think you should learn that because it provides type safety which is not the case when working with ints containing an address. What kind of data are you manipulating ? An array of ints ?
Cédric Moonen Software developer
Charting control [v1.5] OpenGL game tutorial in C++ -
Ok, new edit, i misread you there the first time. LocalAlloc gives you a handle to a memory location, not the memory location itself. Declare your variable as HANDLE, not int, since LocalALloc, unless specified differently, will give you a HANDLE. You have to use LocalLock and LocalUnlock to actually access the memory. But may i ask why you need to use LocalAlloc instead of new or malloc? So basicly, if you have to use LocalAlloc you have to LocalLock(handle), this will give you a void * pointer that points at the memory you allocated, you can feed this to WriteFile (didn't go into WriteFile itself so i assume you know what you are doing with that) and then use LocalUnlock to unlock the memory, also use LocalFree to free it.
modified on Friday, November 21, 2008 6:36 AM
-
LocalAlloc gives you a handle to a memory location, not the memory location itselfActually, that depends on the first parameter. In my case (for Windows Mobile) it always return the actual address, so it is OK.As i said, "unless specified differently". So if you get a pointer at the memory location why do you store it in an int?
-
As i said, "unless specified differently". So if you get a pointer at the memory location why do you store it in an int?