using info from functions to define other functions and structures

[ausairman]

I first posted this here http://www.cplusplus.com/forum/beginner/45574/ but I think it might have been in the wrong section, and maybe I didn't explain it very well so I thought I'd rephrase it here with a bit more detail.

Say I have a function, get_global() that carries out some operations and then returns a value that I will declare as a const int MYGLOBAL. Now, I also want to define a structure called mystruct, whose members will be arrays whose lengths are defined by the MYGLOBAL. and another function called fun_build_mystruct() which will return a structure member of type mystruct. Conceptually, I would do this:

#include<headers.h>

const int get_global() {
    // define my function here
    return MYGLOBAL;
}

const int MYGLOBAL = get_global(); // Can't do this! - we're not in main()

struct mystruct {
    int structarray [MYGLOBAL] // this array size is dependant on the value returned by get_global()
};

mystruct * fun_build_mystruct() {
    mystruct MEMBER;
    return MEMBER;
}

main () {
    //do stuff
    return 0;
}

This however, doesn't work because I can't call get_global() outside of main(). But I can't define my functions inside main, and I can't even declare prototypes because fun_build_mystruct() needs mystruct to be defined before it can be declared. How is this sort of thing normally handled??

[zb0S216C]

1) on line 5, MYGLOBAL is undefined at that point.

2) Line 8 is valid in VCE2010.

3) Line 11 generates an error.

4) On line 16, you return a local instance of mystruct. Don't do this. Still, you don't use the address of operator on MEMBER on line 16.

5) main( ) should be given a return type.

_Wazzak

[hamsterman]

A constant is something you should know at compile time. If you have to call a function to decide its value at run time, use a normal integer and dynamic memory.

Though, as Framework said,

int f(){
   return 5;
}

const int i = f();

works fine on VC++..