C++ Fill a vector in a namespace

I am trying to port the following Python code to C++:

foo.py

import settings.consts as consts

table = [""] * consts.table_size
for idx in range(0, consts.table_size):
    str = consts.lookup[get_by_index(idx)]
    table[idx] = str

def use_table(index):
    return table[index]

It initializes one time a table with the size taken from the settings. Then the table is filled up with values in a for loop. use_table is a simplified function which consumes the table.

Here is my attempt in C++:

foo.h

#ifndef FOO_H
#define FOO_H

#include <vector>
#include <string>
#include "consts.h"

namespace bar {

    std::vector<std::string> table(consts::size_of_table, "");
    int GetByIndex(int a);
    string UseTableable(int index);

} // namespace bar

#endif // FOO_H

foo.cc

string UseTableable(int index)
{
  return table[index];
}

The problem

As far as I know, in C++ the for loop must be in a function. I could make a function to fill up the vector, but when should I call it? Namespaces do not have a constructor, or initialization hooks.

What would be the equivalent architect to the original Python code?

You call the function when you want to initialize the vector.

You can use a lambda function,

std::vector<std::string> table = 
    [](){
            std::vector<std::string> tbl(consts::size_of_table, "");
            for (size_t i = 0; i < tbl.size(); i++) {
                tbl[i] = consts::lookup[GetByIndex(i)];
            }
            return tbl;
    }();

or a named function,

std::vector<std::string> make_table()
{
    std::vector<std::string> tbl(consts::size_of_table, "");
    for (size_t i = 0; i < tbl.size(); i++) {
        tbl[i] = consts::lookup[GetByIndex(i)];
    }
    return tbl;
}

std::vector<std::string> table = make_table();

You can do the initialization in your program's main() function, eg:

foo.h

#ifndef FOO_H
#define FOO_H

#include <vector>
#include <string>

namespace bar {

    extern std::vector<std::string> table;

    void InitTable();
    int GetByIndex(int a);
    std::string UseTable(int index);

} // namespace bar

#endif // FOO_H

foo.cpp

#include "foo.h"
#include "consts.h"

std::vector<std::string> bar::table;

void bar::InitTable()
{
    table.resize(consts::size_of_table, "");
    for(int idx = 0; idx < consts::size_of_table; ++idx) {
        table[idx] = consts::lookup[GetByIndex(idx)];
    }

    /* alternatively:
    table.reserve(consts::size_of_table);
    for(int idx = 0; idx < consts::size_of_table; ++idx) {
        table.push_back(consts::lookup[GetByIndex(idx)]);
    }
    */
}

int bar::GetByIndex(int a)
{
    return ...;
}

string bar::UseTable(int index)
{
  return table[index];
}

main.cpp

#include "foo.h"

int main()
{
    bar::InitTable();
    // use table as needed...
    return 0;
}