CODEWITHSUNDEEP
c++
Mohammad Moghimi
Mohammad Moghimi

Reputation: 4686

How to best initialize a vector of strings in C++?

I generally love python's syntax.

v = ["sds", "bsdf", "dsdfaf"]

What I currently have in C++ looks like this

vector<string> v;
v.push_back("sds");
v.push_back("bsdf");
v.push_back("dsdfaf");

Is there a better/cleaner way to do this? Note that v remains unchanged after initialization. So an array might work too but the problem with array is that I need to also hardcode the length of the array in my code.

char* v[] = {"sds", "bsdf", "dsdfaf"};
for (int i = 0; i < 3; ++i) do_something(v[i]);

EDIT: I don't have C++11. My Compiler is gcc 4.1.2

Upvotes: 8

Views: 15380

Answers (4)

Void - Othman
Void - Othman

Reputation: 3481

Note that v remains unchanged after initialization. So an array might work too but the problem with array is that I need to also hardcode the length of the array in my code.

That's not true. You can get the array size the canonical way one does so like the following:

#include <iostream>

int main()
{
    char const * const v[] = {"sds", "bsdf", "dsdfaf"};

    // Only works when array length is known at compile-time.
    size_t const len = sizeof(v) /sizeof(v[0]);
    for (size_t i = 0; i < len; ++i)
        std::cout << v[i] << '\n';
}

The output is:

$ g++ -Wall foo.cpp ; ./a.out 
sds
bsdf
dsdfaf

Upvotes: 0

Praetorian
Praetorian

Reputation: 109119

C++03 solutions:

Use vector constructor that takes a pair of iterators.

char* arr[] = {"sds", "bsdf", "dsdfaf"};
vector<string> v(arr, arr + sizeof(arr)/sizeof(arr[0]));

Use an array if the length doesn't need to change after initialization. To avoid hardcoding array length use this function template to deduce size

template<typename T, std::size_t N>
std::size_t length_of( T const (&)[N] ) { return N; }

char* v[] = {"sds", "bsdf", "dsdfaf"};
for (int i = 0; i < length_of(v); ++i) do_something(v[i]);

Note that this won't work within a function to which you pass a char **.

Use boost::assign::list_of

using boost::assign::list_of;
std::vector<std::string> v = list_of("sds")("bsdf")("dsdfaf");

Upvotes: 4

Shoe
Shoe

Reputation: 76240

Is there a better/cleaner way to do this?

You can use the brace initialization syntax:

std::vector<std::string> v { "sds", "bsdf", "dsdfaf" };

Note that v remains unchanged after initialization.

You can use an std::array (since C++11):

std::array<std::string, 3> a {{ "sds", "bsdf", "dsdfaf" }};

You'll still have to "hardcode" the number of elements, but it's not dynamic anyway, so you don't lose much.

Upvotes: 2

NPE
NPE

Reputation: 500367

In C++11 you can write:

std::vector<std::string> v{"sds", "bsdf", "dsdfaf"};

Upvotes: 4

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