C++ Fill a vector with another vector

Question

I have two vectors, and I would like to fill the first one with the second. The vectors are declared like this:

vector<Vec3> firstVector;

Where Vec3 is a struct with float x, y, z. I have tried liked this with assign:

secondVector.assign(firstVector.begin(), firstVector.end());

But it stops and complains, that there is problem with the end(). I have also tried pushback, but of course it's not working.

As I read before I should do it with assign, but I don't know how to solve it properly.

EDIT:

The error message with insert and assign are the same:

this 0x00000000 ... std::vector > * const

[size] CXX0030: Error: expression cannot be evaluated
[capacity] CXX0030: Error: expression cannot be evaluated

And it points to Visual Studio's vector file to iterator end to the return. With insert it points to iterator begin.

THE CODE:

The first Vector is also part of a struct:

struct o3DModel
{
    vector<Vec3> v_Vertices;
};

struct Vec3 {
public:
Vec3() {}

Vec3(float X, float Y, float Z)
{
    x = X;
    y = Y;
    z = Z;
}

float x, y, z;
};

I declare the "o3DModel" struct above in my app class like this and send it to my loader class:

o3DModel *tfTable;

void TheApp::Init()
{
    objLoader->ImportOBJ(tfTable, "testcube.obj");
}

The objLoader class, where I successfully fill my "v_Vertices" vector, where "oModel" is the sent "tfTable":

bool OBJLoader::ImportOBJ(o3DModel *oModel, char *strFileName)
{
    FillObjData(oModel);
    ...
    return true;
}

void OBJLoader::FillObjData(o3DModel *oModel)
{
    oModel->v_Vertices.insert(oModel->v_Vertices.begin(), v_Vertices.begin(), v_Vertices.end());
    // This here with insert
    outFile2 << oModel->v_Vertices[0].x << "\n";
}

Hope this helps.

Your code should work (although I disagree that you "should do it with assign"). Can you post the exact error message you receive? — Robᵩ, Mar 28 '12 at 17:01
How is `secondVector` declared, and what exactly is the error message? (Also, a simple `secondVector = firstVector` would do the same thing). — Mike Seymour, Mar 28 '12 at 17:02
I see I should post the error message. I edit my question with it. — matthew3r, Mar 28 '12 at 17:08
You are dereferencing a NULL pointer. The problem is not in the code that you have shown us, but in the code that you haven't. Please reduce your program to the smallest possible program that still demonstrates the error, and then post that very small, **complete** program into your question. See http://sscce.org/ for more information. — Robᵩ, Mar 28 '12 at 17:13
If not the complete program, but I will reduce everything and post it. — matthew3r, Mar 28 '12 at 17:16
Possible duplicate of [fast way to copy one vector into another](https://stackoverflow.com/questions/644673/fast-way-to-copy-one-vector-into-another) — hmofrad, Jul 19 '18 at 22:11

Robᵩ · Answer 1 · 2012-03-28T17:09:56.340

8

If you want secondVector to take on all of the values of firstVector and no others,

secondVector = firstVector;

If you want each of the elements of firstVector to be added to the end secondVector:

secondVector.insert(secondVector.end(), 
                    firstvector.begin(), firstVector.end());

If you want each of the elements of firstVector to be added to the beginning of secondVector:

secondVector.insert(secondVector.begin(), 
                    firstVector.begin(), firstVector.end());

edited Mar 28 '12 at 17:09

answered Mar 28 '12 at 16:57

Robᵩ

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There is a problem with begin, but as you wrote I will post the code in the question. – matthew3r Mar 28 '12 at 17:17

score 4 · Answer 2 · answered Mar 28 '12 at 16:57

4

Or if you don't want to do it in the ctor use

secondVector = firstVector

answered Mar 28 '12 at 16:57

Martin Beckett

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@Robᵩ - yes sorry was thing of something else, anyway no reason not use '=' – Martin Beckett Mar 28 '12 at 17:00

Kiril · Answer 3 · 2012-03-28T17:11:05.327

2

This should work:

vector<Vec3> secondVector(firstVector.begin(), firstVector.end());

That's the case when you're interested in using the vector constructor.

edited Mar 28 '12 at 17:11

answered Mar 28 '12 at 16:56

Kiril

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@Robᵩ ah... yes, typo indeed :). – Kiril Mar 28 '12 at 17:00
My hearth hurts every time I see "cplusplus.com" in SO post. Use cppreference.com instead. – Griwes Mar 28 '12 at 17:03
@Griwes yah, they need to improve their pagerank... blame Google! – Kiril Mar 28 '12 at 17:09
@Griwes Except that *cppreference*, although maybe more formally correct, misses documentation for many simple things. They support C++11, though. – Christian Rau Mar 28 '12 at 17:09

score 1 · Answer 4 · answered Mar 28 '12 at 16:58

1

You second vector needs to be declared as a vector of vectors of Vec3 strucs.

    vector<vector<Vec3>> secondVector;
    secondVector.push_back(firstVector);

answered Mar 28 '12 at 16:58

TVOHM

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score -1 · Accepted Answer · answered Mar 31 '12 at 14:08

Okay, I have solved it, but with a little roundabout. In FillObjData I have created a new Vec3, created an if, gived the first vector x, y, z coordinate to the new Vec3, and pushed the Vec3 into the vector. And when I declared my struct I have declared it real not as a pointer. Now it works perfectly.

C++ Fill a vector with another vector

5 Answers5