A Variable variable name?

Hi guys!
I'm looking for a way to get something like this running: i want to pass to a function a argument whose name would be variable. A little more specific: there's this function

Code:

---

LoadSomething(int nvm, int hereWeAre)

---

- it loads some graphics based on variable hereWeAre - basicly passing hereWeAre to the function would load graphics hereWeAre.bmp. Unfortunetaly I have hundreds of graphics to load so i want to do it in a loop - but here the problem appears: I dunno how to make the progam evaluate, lets say, a string variable saying hereWeAre2 so i can pass the value of the string as the name of the integer var needed in this function.
Dunno if i made the problem clear enough. But hope someone can tell me if this is possible.
Thanks,
Sakurazuka

Quote:

---

Originally Posted by sakurazuka

i want to pass to a function a argument whose name would be variable.

---

Why don't you pass a String instead, like

LoadSomething(int nvm, String loadName)

Then you can do

LoadSomething(someInt, "hereWeAre.bmp");

If this isn't possible there's some additional condition you haven't revealed.

Well, the exact behavior I want to emulate would be something like this (sorry for the PHP style - but it shows exactly what i want/need to do - at least i think so)

Code:

---


$pref = hereWeAre
$suf = 1
$name = $pref+$suf
LoadSomething(0, $($name))

---

Quote:

---

Originally Posted by nuzzle

Why don't you pass a String instead, like

LoadSomething(int nvm, String loadName)

Then you can do

LoadSomething(someInt, "hereWeAre.bmp");

If this isn't possible there's some additional condition you haven't revealed.

---

Unfortunetaly - it doesn't work that way - tried that. I think it's because each graphic file has a distinct integer attached to it - and an external integer variable is being created for the file. So i have to pass the integer variable hereWeAre as a parameter (corresponding to the file hereWeAre.bmp) - the value of which i don't know :(.

I tried to solve this problem with some #define macros - but seem to be stuck at a point where the macro does not switch to integer:

Code:

---

#define replace( n )  ("_0_0" #n "_Bitmap")
int iFrame = 1;
LoadSomething(0, replace( iFrame ));

---

the result of replace( iFrame )) is always

Code:

---

_0_0iFrame_Bitmap

---

instead of

Code:

---

_0_01_Bitmap

---

Preprocessor macros run before your program is even compiled, so it cannot possibly read variable contents. Besides, macros are evil. Just ask/look for the correct way to do string concatenation in c++:

You can use a stringstream to stream all the variables into a string, and use that:

Code:

---

#include <iostream>
#include <string>
#include <sstream>

void load_something(const std::string& bmp_name, int bmp_number)
{
    std::ostringstream oss;
    oss << bmp_name << "-" << bmp_number << ".bmp";

    std::string file_name = oss.str();
    //do_it(file_name.c_str());

    std::cout << file_name << std::endl;
}

int main()
{
    load_something("my_image", 5);
}

---

This print out "my_image-5.bmp" on my machine.

The idea is that once the stream is full, you can extract a string from it, and from there, you can do whatever you want with it, or even its underlying c-style char array: c_str.

Yes use strings or put a large switch statement in the LoadSomething function..
But seriously, just learn how to use strings.

You could use a std::map<int, std::string>.

Well, as i checked the ostringstream and string constructs, and i guess the templates as well, are not supported on the architecture I'm writing at. I guess that only leaves me with the macros. I found a promising example but it doesn't do the things it's suppose to. Here's the link
http://msdn.microsoft.com/en-us/libr...=VS.80%29.aspx
It works as I stated earlier. Dunno why, though

Quote:

---

Originally Posted by sakurazuka

Dunno why, though

---

Ok, nevermind - as monarch_dodra wrote before, it's not interpreted in the program but earlier. In the example they use a const value 9 as a parameter. It can't possibly work the way I wanted it to. **** it, I don't see a way out of this except the tiresome switch part :/. Blast - anyone got any ideas?

As I said, forget macros. If you want to convert a number to a char array, you can use the not so standard but widely supported itoa function.

BTW, all architectures support templates. You are writing plain old C, or you are using a crap compiler. Either way, I would look into my compiler's doc to see if it provides any kind of string like object.

Quote:

---

Originally Posted by monarch_dodra

If you want to convert a number to a char array, you can use the not so standard but widely supported itoa function.

---

sprintf and snprintf are alternatives from the C standard library, and have been borrowed by the C++ standard library.

Quote:

---

Originally Posted by monarch_dodra

or you are using a crap compiler.

---

Nah man, it's just a homebrew compiler for a handheld. Maybe that makes it crappy but it's the only one there is. Anyway, I just wrote a bash script to edit the source file and create a really huge switch statement. Esthetically kinda sucks, but hey - it does the job...

Quote:

---

Originally Posted by sakurazuka

Well, as i checked the ostringstream and string constructs, and i guess the templates as well, are not supported on the architecture I'm writing at. I guess that only leaves me with the macros. I found a promising example but it doesn't do the things it's suppose to. Here's the link
http://msdn.microsoft.com/en-us/libr...=VS.80%29.aspx
It works as I stated earlier. Dunno why, though

---

Looks like you got a wrong footing and digging at all the wrong places.
Variable variables in PHP is a dynamic binding. Pointers drive the dynamic bindings in C++ so that's where you will likely find the answer not in the stringstream/macro or anything thereof. Once you get into it, you will see why C++ doesn't support - or why it is redundant - some of the things offered in PHP like string inter-polaraity or mainly variable variables.

Bottom line:
For starters, go with what ninja9578 said.