cannot appear in a constant-expression (list)

[hooshdar3]

Hi.
Why do I get the error

'rec' cannot appear in a constant-expression

?

I have the following definitions:

  ...  string rec[6];
    list<rec> musicList;
...

[Lachlan Easton]

list (I'm assuming it's a std::list) expects a typename for its (first) template parameter. You're giving it an array of strings.

[hooshdar3]

Yes, an std::list.
What should I do?

[Lachlan Easton]

It depends on what you want to do, which you haven't specified. I'm going to assume you want to make a list of strings, that would be list<string> musicList; as string names the type of object to make a list of.

[hooshdar3]

I am going to make a list of 6 string( an array of 6 strings.I can make an array of lists of strings, but that is not what I am up to

[firedraco]

You can try using std::array:

std::array<std::string, 6> rec;
std::list< std::array<std::string, 6> > musicList;

This requires C++11 libraries, so you might need to enable them.

[hooshdar3]

What's wrong with:

struct A {
   int array[2];
} ;

std::list <A> alist;

? I want something C++ 98

[giblit]

Nothing is wrong with that. But, there is something wrong with trying to use a variable instead of a type as the template type.

Though how did you go from an array of 6 strings to an array of 2 ints :P

Also, if that is something you want then do it we can't stop you.

[hooshdar3]

You don't stop me, the compiler does.

Here is What I did:

    string rec[3];
    
    rec[0] = "ali";
    rec[1] = "hasan";
    rec[2] = "hossein";

std::list <string[3]> alist;
alist.push_back(rec);

But the last line errs.....................

[kbw]

You don't want a list of an array of 3 strings, you want a list or strings, right? So that gives you:

std::list<std::string> alist;
alist.push_back("ali");
alist.push_back("hasan");
alist.push_back("hossein");

[hooshdar3]

kbw (7000)
You don't want a list of an array of 3 strings, you want a list or strings, right?

No.I want a list of arrays. I mean each line of list should have 3 parts

[TwilightSpectre]

A list of arrays of strings?

#include <string>
#include <list>

// either
#include <array>
std::list<std::array<std::string, 3>> alist; // list of arrays of 3 strings

// or (C++98)
#include <vector>
std::list<std::vector<std::string>> alist; // list of dynamic arrays of strings 

EDIT: sorry, missed your earlier post about C++11. But, you should consider using it - it has been around for 3 years now, most compilers should support it.

[AbstractionAnon]

If you want something C++98, then the struct approach you had earlier will work if you use strings instead of ints.

struct A
{  string rec[3];
};
A                   a;
std::list<A>  alist;  

a.rec[0] = "ali";
a.rec[1] = "hasan";
a.rec[2] = "hossein";
alist.push_back (a); 
std::list<A>::iterator iter = alist.begin();
std::cout << iter->rec[0] << std::endl;
std::cout << iter->rec[1] << std::endl;
std::cout << iter->rec[2] << std::endl;

[hooshdar3]

AbstractionAnon (2459)
If you want something C++98, then the struct approach you had earlier will work if you use strings instead of ints.

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struct A
{ string rec[3];
};
A a;
std::list<A> alist;

a.rec[0] = "ali";
a.rec[1] = "hasan";
a.rec[2] = "hossein";
alist.push_back (a);
std::list<A>::iterator iter = alist.begin();
std::cout << iter->rec[0] << std::endl;
std::cout << iter->rec[1] << std::endl;
std::cout << iter->rec[2] << std::endl;

I copied your code and pasted it into my main() function.This is the error I get:

21 G:\Test_suite\HW2_Hooshdaran.cpp `main()::A' uses local type `main()::A'

[AbstractionAnon]

I got no such error.

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#include <string> #include <list> #include <iostream> using namespace std; struct A { string rec[3]; }; int main () { A a; std::list<A> alist; a.rec[0] = "ali"; a.rec[1] = "hasan"; a.rec[2] = "hossein"; alist.push_back (a); std::list<A>::iterator iter = alist.begin(); std::cout << iter->rec[0] << std::endl; std::cout << iter->rec[1] << std::endl; std::cout << iter->rec[2] << std::endl; }

ali hasan hossein Press any key to continue . . .

[hooshdar3]

Thanks.I also get no error now that I moved the definition of A outside of main() scope.

[AbstractionAnon]

It should make no difference if A is defined inside or outside of the main scope. Just as long as it's defined before the use of it at line 11.

[giblit]

If it is defined inside of a function is it scoped to that function as the "error" or "warning" you got. Meaning you can't use it outside of that function.