Some proble on " merge() on vector "

Hi, guys~
I randomly tapped some *int* number into 2 text files:
test_1.txt:
3 20 16 13 12 11 10 9 20 36 15 1547 13 46 156741 13461 6541 3134564 13
1564 1315 464 13247 1549
test_2.txt:
45 6413 21 456 461 38 794 131 654 64 4321 314 654 615 3134654 4564 1
31 346 54

my code is below:
/////////////////////////////////////////////////////////////////////////////////////////////////////////////
#include<iostream>
#include<fstream>
#include<vector>
using namespace std;

int main()
{
    ifstream fin_1("test_1.txt"), fin_2("test_2.txt");
    int ii;
    vector<int> vi_1, vi_2;
    while(fin_1>>ii)
        vi_1.push_back(ii);
    sort(vi_1.begin(), vi_1.end());
                //to check whether vi_1 is right
    for(vector<int>::iterator iter=vi_1.begin(); iter!=vi_1.end(); +
+iter)
        cout<<*iter<<'\t';
    cout<<endl;

    while(fin_2>>ii)
        vi_2.push_back(ii);
    sort(vi_2.begin(), vi_2.end());
    for(vector<int>::iterator iter=vi_2.begin(); iter!=vi_2.end(); +
+iter)
        cout<<*iter<<'\t';
    cout<<endl;

    vector<int> vi_3;

                //I don't know whether this is needed.*reserve*
    vi_3.reserve(100);

                // could I replace *vi_3.begin()* to *vi_1.begin()*?
I just wanna use vi_1 .
    merge(vi_1.begin(), vi_1.end(), vi_2.begin(), vi_2.end(),
vi_3.begin());

                // to know the size of vi_3
    int count;
    for(vector<int>::iterator iter=vi_3.begin(); iter!=vi_3.end(); +
+iter)
    {
        ++count;
        cout<<*iter<<endl;
    }
                // the *count* came out to be 206856 . I don't know
why.
    cout<<count<<endl;
}
//: IDE: DEV C++ 4.9.9.2
//:~
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////
But this didn't work.
Maybe the code is not right. My meant to merge vi_1 and vi_2 to
vi_1.

I wrote this source code to test the *merge()* problem which also
appeared in anothe project.

Thanks for your advices !

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