Initialize a string vector in header file

Question

I am doing a bit from Stroustrup's "Principles and practice" chapter 10, where he offers to create a table for converting numbers of months to their names and vice versa. That table is in a form of a string vector, which is then used by several functions declared in the header file of the program. I tried to go an easy way and declare + init the vector in the same header, so that all the functions could see it:

std::vector<std::string> monthNames(12);
monthNames[0] = "jan";
monthNames[1] = "feb";
monthNames[2] = "mar";
monthNames[3] = "apr";
monthNames[4] = "may";
monthNames[5] = "jun";
monthNames[6] = "jul";
monthNames[7] = "aug";
monthNames[8] = "sep";
monthNames[9] = "oct";
monthNames[10] = "nov";
monthNames[11] = "dec";

Now G++ does not seem to understand what I'm trying to do:

In file included from temperature.cpp:1:
./Temperature.h:48:1: error: C++ requires a type specifier for all declarations
monthNames[0] = "jan";
^~~~~~~~~~
./Temperature.h:49:1: error: C++ requires a type specifier for all declarations
monthNames[1] = "feb";

...

I understand in general, that declaring a global vector in a header is a poor practice, but in this example it seems to be a reasonable substitute for 12 {if...elses} in the functions that convert nums to month names and vice versa:

    const std::string& intToMonth(int num) {
    if ( num < 1 || num > 12 )
        throw BadMonthException();

    return monthNames[num-1];
    }

So I have two questions:

1) Why would compiler not let me initialize the vector?

2) Is there a sexier way to make it all work (without a global vector)?

Please provide a [MCVE](http://stackoverflow.com/help/mcve). Also, what compiler and Standard library versions do you use? — Ivan Aksamentov - Drop, Mar 13 '15 at 11:35
@Blacktempel: It's 2015. Every C++ question is by default at least a C++11 question. — Lightness Races in Orbit, Mar 13 '15 at 11:35
_"I understand in general, that declaring a global vector in a header is a poor practice"_ The problem is not that the vector is global, it's that you try to run code (the 12 assignments into the vector) at global scope, and only declarations and definitions are allowed at global scope, not statements. — Jonathan Wakely, Mar 13 '15 at 11:40
@Drop All of you forget the people who cannot use C++11 or higher standards yet. If the question is not tagged C++11 or higher, then you can't answer or comment with C++11 or higher. — Blacktempel, Mar 13 '15 at 11:41
I'm not sure if this is really dup of that question. My bet is `monthNames` was just declared in another scope or a typo or whatever. — Ivan Aksamentov - Drop, Mar 13 '15 at 11:41
And also [c++98] ;) Unfortunately there is no [c-with-classes] tag ;( — Ivan Aksamentov - Drop, Mar 13 '15 at 11:46
@Blacktempel: And? So? Therefore? It's not tagged C++03, either. — Lightness Races in Orbit, Mar 13 '15 at 12:05
@Blacktempel: There will always be people who have constraints. They should mark those constraints on the question. If they do not do so, we will assume that they are using the C++ of today, not the C++ of yesterday. Nobody's "forgetting" anything. Your statement _"If the question is not tagged C++11 or higher, then you can't answer or comment with C++11 or higher"_ is just plain wrong. — Lightness Races in Orbit, Mar 13 '15 at 12:06
@Blacktempel and you forget the people who can use C++ or higher standards already. If there is a C++11 answer, they will appreciate it. No one forbids non-C++11 answers. — R. Martinho Fernandes, Mar 13 '15 at 12:08
Sorry for not mentioning in the question, but it's not C++11 — Denys Triasunov, Mar 13 '15 at 12:26

score 1 · Answer 1 · answered Mar 13 '15 at 11:35

Providing the include file isn't included more than once, you can use an anonymous namespace and an initialisation list, something like:

 namespace {
    std::vector<std::string> monthNames{ "jan", "feb", "mar", "apr", "may", "jun", "jul", "aug", "sep", "oct", "nov", "dec"};
}

tonso · Answer 2 · 2015-03-13T11:42:05.510

You can try something like this (works for cpp standards older than c++11):

const std::string _monthNames[] = { "jan", "feb", ... };
std::vector<std::string> monthNames(_monthNames,
                                    _monthNames+sizeof(_monthNames)/sizeof(std::string));

Regarding your questions:

The statements cannot be used as declarations according to C++ grammar rules.
Consider using static function variables -- the variables that are visible only in the scope of the function, but having the same lifetime as global variables.

Initialize a string vector in header file

2 Answers2