How to declare an array of strings in C++?

Question

I am trying to iterate over all the elements of a static array of strings in the best possible way. I want to be able to declare it on one line and easily add/remove elements from it without having to keep track of the number. Sounds really simple, doesn't it?

Possible non-solutions:

vector<string> v;
v.push_back("abc");
b.push_back("xyz");
for(i=0; i < v.size(); i++) cout << v[i] << endl;

Problems - no way to create the vector on one line with a list of strings

Possible non-solution 2:

    string list[] = {"abc", "xyz"};

Problems - no way to get the number of strings automatically (that i know of).

There must be an easy way of doing this ...

Answer 1

The boost assign library seems to be exactly what you are looking for. It makes assigning constants to containers easier than ever.

Answer 2

Problems - no way to get the number of strings automatically (that i know of).

There is a bog-standard way of doing this, which lots of people (including MS) define macros like arraysize() for:

#define arraysize(ar)  (sizeof(ar) / sizeof(ar[0]))

Answer 3

Here's an example:

#include <iostream>
#include <string>
#include <vector>
#include <iterator>
using namespace std;

int main() {
    const char* const list[] = {"zip", "zam", "bam"};
    const size_t len = sizeof(list) / sizeof(list[0]);
    for (size_t i = 0; i < len; ++i) {
        cout << list[i] << "\n";
    }
    const vector<string> v(list, list + len);
    copy(v.begin(), v.end(), ostream_iterator<string>(cout, "\n"));
}

Answer 4

You can concisely initialize a vector<string> from a statically-created char* array:

char* strarray[] = {"hey", "sup", "dogg"};
vector<string> strvector(strarray, strarray + 3);

This copies all the strings, by the way, so you use twice the memory. You can use Will Dean's suggestion to replace the magic number 3 here with arraysize(str_array) -- although I remember there being some special case in which that particular version of arraysize might do Something Bad (sorry I can't remember the details immediately). But it very often works correctly.

Also, if you're really gung-ho about the one line thingy, you can define a variadic macro so that a single line such as DEFINE_STR_VEC(strvector, "hi", "there", "everyone"); works.

Answer 5

C++ 0x is introducing initialization lists which will allow you to do:

std::vector<std::string> v = {"Hello", "World"};

Probably doesn't help you now. Although GCC 4.4 apparently supports this already.

Answer 6

Instead of that macro, might I suggest this one:

template<typename T, int N>
inline size_t array_size(T(&)[N])
{
    return N;
}

#define ARRAY_SIZE(X)   (sizeof(array_size(X)) ? (sizeof(X) / sizeof((X)[0])) : -1)

1) We want to use a macro to make it a compile-time constant; the function call's result is not a compile-time constant.

2) However, we don't want to use a macro because the macro could be accidentally used on a pointer. The function can only be used on compile-time arrays.

So, we use the defined-ness of the function to make the macro "safe"; if the function exists (i.e. it has non-zero size) then we use the macro as above. If the function does not exist we return a bad value.

Answer 7

#include <boost/foreach.hpp>

const char* list[] = {"abc", "xyz"};
BOOST_FOREACH(const char* str, list)
{
    cout << str << endl;
}

Answer 8

One possiblity is to use a NULL pointer as a flag value:

const char *list[] = {"dog", "cat", NULL};
for (char **iList = list; *iList != NULL; ++iList)
{
    cout << *iList;
}

Answer 9

Tried to upvote Craig H's answer that you should use boost::assign, but I have no rep :(

I encountered a similar technique in the first article I ever read by Andrei Alexandrescu in C/C++ Users Journal, Vol 16, No 9, September 1998, pp. 73-74 (have the full citation because it's in the comments of my implementation of his code I've been using ever since).

Templates are your friend.

Answer 10

You can use the begin() and end() functions from the Boost range library to easily find the ends of a primitive array, and unlike the macro solution, this will give a compile error instead of broken behaviour if you accidentally apply it to a pointer.

const char* array[] = { "cat", "dog", "horse" };
vector<string> vec(begin(array), end(array));

Answer 11

SORRY FOR GOING off the topic..... i was trying to find how could i define string array i find it ..... but i don't know how could i compare them.. BEcause one is 2d string pointer and one is just a pointer

Answer 12

#include <iostream>
#include <string>
#include <vector>
#include <boost/assign/list_of.hpp>

int main()
{
    const std::vector< std::string > v = boost::assign::list_of( "abc" )( "xyz" );
    std::copy(
        v.begin(),
        v.end(),
        std::ostream_iterator< std::string >( std::cout, "\n" ) );
}