Passing a structure array in a function

[wboustany]

Hi all,

I have been struggling with this for hours....

I have defined a structure:

struct unit {
		ALLEGRO_BITMAP *pic;
		char *name;
		int strength, hp, initiative;} ground_unit[4];

	ground_unit[1].name="Abrams";
	ground_unit[1].strength=150;
	ground_unit[1].hp=1000;
	ground_unit[1].initiative=2;
	ground_unit[2].name="Legionnaire";
	ground_unit[2].strength=50;
	ground_unit[2].hp=500;
	ground_unit[2].initiative=5;
	ground_unit[3].name="Flower";
	ground_unit[3].strength=250;
	ground_unit[3].hp=3000;
	ground_unit[3].initiative=1;

two variables:

int l=0, m=1;

and trying to set up the following function....

void draw_all(int &l, int &m, struct unit ground_unit[4]){
						al_draw_textf(font1, al_map_rgb(0,255,255), 220, 220,0, "Unit: %s", ground_unit[l].name); 
						al_draw_textf(font1, al_map_rgb(0,255,255), 420, 220,0, "Unit: %s", ground_unit[m].name); 

}

I know that you may not be familiar with allegro, but my problem is purely in c/c++ and is about the two last lines.

So basically I want the function to draw "ground_unit[0].name" and "ground_unit[1].name". However I am completely lost, I have tried the following combinations:

void draw_all(int l, int m, struct unit ground_unit[4]){
						al_draw_textf(font1, al_map_rgb(0,255,255), 220, 220,0, "Unit: %s", ground_unit[l].name); 
						al_draw_textf(font1, al_map_rgb(0,255,255), 420, 220,0, "Unit: %s", ground_unit[m].name); 

}

void draw_all(struct unit ground_unit[4]){
						al_draw_textf(font1, al_map_rgb(0,255,255), 220, 220,0, "Unit: %s", ground_unit[&l].name); 
						al_draw_textf(font1, al_map_rgb(0,255,255), 420, 220,0, "Unit: %s", ground_unit[&m].name); 

}

void draw_all(int &l, int &m, struct unit ground_unit[4]){
						al_draw_textf(font1, al_map_rgb(0,255,255), 220, 220,0, "Unit: %s", ground_unit[&l].name); 
						al_draw_textf(font1, al_map_rgb(0,255,255), 420, 220,0, "Unit: %s", ground_unit[&m].name); 

}

void draw_all(int &l, int &m, struct unit ground_unit[4].name){
						al_draw_textf(font1, al_map_rgb(0,255,255), 220, 220,0, "Unit: %s", ground_unit[l].name); 
						al_draw_textf(font1, al_map_rgb(0,255,255), 420, 220,0, "Unit: %s", ground_unit[m].name); 

}

void draw_all(int &l, int &m, struct unit char ground_unit[4].name){
						al_draw_textf(font1, al_map_rgb(0,255,255), 220, 220,0, "Unit: %s", ground_unit[l].name); 
						al_draw_textf(font1, al_map_rgb(0,255,255), 420, 220,0, "Unit: %s", ground_unit[m].name); 

}

None are working....any insight would be very helpful....

For the first try I get:

1>c:\users\wboustany\desktop\project_allegro\pic display test\pic display test\main.cpp(23): error C2036: 'unit []' : unknown size
1>c:\users\wboustany\desktop\project_allegro\pic display test\pic display test\main.cpp(23): error C2027: use of undefined type 'unit'
1> c:\users\wboustany\desktop\project_allegro\pic display test\pic display test\main.cpp(19) : see declaration of 'unit'
1>c:\users\wboustany\desktop\project_allegro\pic display test\pic display test\main.cpp(23): error C2228: left of '.name' must have class/struct/union
1>c:\users\wboustany\desktop\project_allegro\pic display test\pic display test\main.cpp(24): error C2036: 'unit []' : unknown size
1>c:\users\wboustany\desktop\project_allegro\pic display test\pic display test\main.cpp(24): error C2027: use of undefined type 'unit'
1> c:\users\wboustany\desktop\project_allegro\pic display test\pic display test\main.cpp(19) : see declaration of 'unit'
1>c:\users\wboustany\desktop\project_allegro\pic display test\pic display test\main.cpp(24): error C2228: left of '.name' must have class/struct/union

Please help and thanks,

Wissam

[rishabhagl]

Pass the structure by reference. Prototype of draw_all should be
void draw_all(int l, int m, struct unit *ground_unit)
{
.....
}

Now do whatever you need to do in the function.

[hamsterman]

It should work (the first ones).
Look at this:

#include <iostream>
#include <string>

struct str{
    std::string s;
} array[] = {"hello", "world"};

void print(int a, int b, struct str arr[]){
    std::cout << arr[a].s << " " << arr[b].s;
}

int main(){
    print(0, 1, array);
    std::cin.get();
    return 0;
}

Compile this. It should work. Then try to find the differences.
By the way, could it be that you didn't define unit before the function, only forward declared it?

[wboustany]

Thank you very much guys. Hamsterman I have built on your example and now it works !

However this spanned several questions important for my understanding.

If I put the structure globally (and not in the main loop as before) it does work well....

	struct unit {
	ALLEGRO_BITMAP *pic;
	char *name;
	int strength, hp, initiative;} ground_unit[4];

void draw_all(int l, int m, ALLEGRO_FONT *font1, struct unit ground_unit[]){
						al_draw_textf(font1, al_map_rgb(0,255,255), 220, 220,0, "Unit: %s", ground_unit[l].name); 
						al_draw_textf(font1, al_map_rgb(0,255,255), 420, 220,0, "Unit: %s", ground_unit[m].name);  }

int main(int argc, char *argv[]) { blablabla

does not show any error!

However this does:

void draw_all(int l, int m, ALLEGRO_FONT *font1, struct unit ground_unit[]){
						al_draw_textf(font1, al_map_rgb(0,255,255), 220, 220,0, "Unit: %s", ground_unit[l].name); 
						al_draw_textf(font1, al_map_rgb(0,255,255), 420, 220,0, "Unit: %s", ground_unit[m].name);  }

	struct unit {
	ALLEGRO_BITMAP *pic;
	char *name;
	int strength, hp, initiative;} ground_unit[4];

int main(int argc, char *argv[]) { blablabla

why ?

also, is there a way to declare the structure locally and still be able to use it in a function ?

Many thanks for your help guys,

Regards,

Wissam

[hamsterman]

You have to define stuff before you use it. That way the compiler only has to read your code once thus saving compilation time. Note: read this (4th, 5th sections) a bit http://www.cplusplus.com/forum/articles/10627/ to know forward declaring.

You can declare functions localy, but then you'll only be able to use them in that scope.