C++ vector literals, or something like them

Question

I'm writing some code against a C++ API that takes vectors of vectors of vectors, and it's getting tedious to write code like the following all over the place:

vector<string> vs1;
vs1.push_back("x");
vs1.push_back("y");
...
vector<string> vs2;
...
vector<vector<string> > vvs1;
vvs1.push_back(vs1);
vvs1.push_back(vs2);
...
vector<vector<string> > vvs2;
...
vector<vector<vector<string> > > vvvs;
vvvs.push_back(vvs1);
vvvs.push_back(vvs2);
...

Does C++ have a vector literal syntax? I.e., something like:

vector<vector<vector<string>>> vvvs = 
    { { {"x","y", ... }, ... }, ... }

Is there a non-builtin way to accomplish this?

score 43 · Accepted Answer · edited Aug 12 '16 at 12:24

43

In C++0x you will be able to use your desired syntax:

vector<vector<vector<string> > > vvvs = 
    { { {"x","y", ... }, ... }, ... };

But in today's C++ you are limited to using boost.assign which lets you do:

vector<string> vs1;
vs1 += "x", "y", ...;
vector<string> vs2;
...
vector<vector<string> > vvs1;
vvs1 += vs1, vs2, ...;
vector<vector<string> > vvs2;
...
vector<vector<vector<string> > > vvvs;
vvvs += vvs1, vvs2, ...;

... or using Qt's containers which let you do it in one go:

QVector<QVector<QVector<string> > > vvvs =
    QVector<QVector<QVector<string> > >() << (
        QVector<QVector<string> >() << (
            QVector<string>() << "x", "y", ...) <<
            ... ) <<
        ...
    ;

The other semi-sane option, at least for flat vectors, is to construct from an array:

string a[] = { "x", "y", "z" };
vector<string> vec(a, a + 3);

edited Aug 12 '16 at 12:24

feedc0de

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answered Apr 16 '09 at 21:26

4

I would recommend using an automated way of retrieving the array size, as the one posted by litb here: http://stackoverflow.com/questions/437150/can-someone-explain-this-template-code-that-gives-me-the-size-of-an-array – David Rodríguez - dribeas Apr 16 '09 at 21:32
2

Yep sure. Didnt wanna complicate the answer. – Apr 16 '09 at 21:33
C++0x is now a thing, and has been renamed c++11 – Antony Aug 21 '20 at 14:06

score 5 · Answer 2 · answered Apr 16 '09 at 21:26

5

Check out Boost assign library.

answered Apr 16 '09 at 21:26

Fred Larson

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score 4 · Answer 3 · answered Apr 16 '09 at 21:28

4

Basically, there's no built-in syntax to do it, because C++ doesn't know about vectors ether; they're just from a convenient library.

That said, if you're loading up a complicated data structure, you should load it from a file or something similar anyway; the code is too brittle otherwise.

answered Apr 16 '09 at 21:28

Charlie Martin

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not only should such a structure not be hardcoded, but I think the fact that such nested vectors are being manipulated directly is a code smell... there should probably be a class encapsulating some or all of that. – rmeador Apr 16 '09 at 22:09
1

STL is not just a _convenient_ library, it's a **standard** library. C++ is built in layers, but that doesn't mean that the pieces were built in a vacuum. – Trade-Ideas Philip Jan 06 '14 at 17:56
1

You're right, I don't find STL all that convenient a library. – Charlie Martin Jan 06 '14 at 22:18
@CharlieMartin Pre-C++11, I would agree. Nowadays? Not at all. – minexew Apr 10 '16 at 14:15
1

Observe the date on the question. – Charlie Martin Apr 10 '16 at 16:50

C++ vector literals, or something like them

3 Answers3

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