c++ MFC slow runtime with 2D vector - c++

Question

I recently finished writing what I consider my "main.cpp" code in a Win32 Console project. It builds the solution perfectly and the external release version runs and completes within like 30 seconds, which is fast for the number of calculations it does.
When I use my MFC built UI made with just 1 standard dialog box for some simple float inputs, the program that ran fine by itself gets hung up when it has to create and calculate some 2D-vectors.
std::mt19937 generator3(time(0));
static uniform_01<std::mt19937> dist3(generator3);
std::vector<int> e_scatter;
for (int i = 0; i <= n; i++)
{
if (dist3() >= perc_e)
{
e_scatter.push_back(1);
// std::cout << e_scatter[i] << '\n';
// system("pause");
}
else
{
e_scatter.push_back(0);
// std::cout << e_scatter[i] << '\n';
// system("pause");
}
}
string fileName_escatter = "escatter.dat";
FILE* dout4 = fopen(fileName_escatter.c_str(), "w");
for (int i = 0; i <= n; i++)
{
fprintf(dout4, "%d", e_scatter[i]);
fprintf(dout4, "\n");
// fprintf(dout2, "%f", e_scatter[i]);
// fprintf(dout2, "\n");
};
fclose(dout4);
std::vector<vector<float>> electron;
// std::vector<float> angle;
**randutils::mt19937_rng rng2;
std::vector<float> rand_scatter;
for (int i = 0; i <= n; i++)
{
std::vector<float> w;
electron.push_back(w);
rand_scatter.push_back(rng2.uniform(0.0, 1.0));
for (int j = 0; j <= 2000; j++)
{
if (e_scatter[i] == 0)
{
electron[i].push_back(linspace[j] * (cos((rand_scatter[i] * 90) * (PI / 180))));
//electron[i][j] == abs(electron[i][j]);
}
else
{
electron[i].push_back(linspace[j]);
};
};
};**
More specifically it does not get past a specific for loop and I am forced to close it. I've let it run for 20 minutes to see if it was just computing things slower, but still got 0 output from it. I am not that great at the debugging part of code when I have this GUI from MFC since I dont have the console popping up.
Is there something that I am missing when I try to use MFC for the gui and large 2D vectors?
The first loop calculates and spits out an output file 'escatter.dat' after its finished but the second set of loops never finishes and the memory usage keeps ramping up.
linspace[i] is calculated before all of this code and is just a vector of 2001 numbers that it uses to populate the std::vector> electron vector in the double for loops.
Ive included this http://pastebin.com/i8A7t38K link to the MFC part of the code that I was using to not make this post really long to read.
Thank you.

Answer 1

I agree that the debugging checks are the major problem.
But if your program is running 30 seconds, n must be big.
You may consider optimizing your code for reducing memory allocations, by preallocating memory using vector::reserve;
std::vector<vector<float>> electron;
// std::vector<float> angle;
**randutils::mt19937_rng rng2;
std::vector<float> rand_scatter;
electron.reserve(n+1); // worth for big n
rand_scatter.reserve(n+1); // worth for big n
for (int i = 0; i <= n; i++)
{
std::vector<float> w;
electron.push_back(w);
rand_scatter.push_back(rng2.uniform(0.0, 1.0));
electron[i].reserve(2000+1); // really worth for big n
for (int j = 0; j <= 2000; j++)
{
if (e_scatter[i] == 0)
{
electron[i].push_back(linspace[j] * (cos((rand_scatter[i] * 90) * (PI / 180))));
//electron[i][j] == abs(electron[i][j]);
}
else
{
electron[i].push_back(linspace[j]);
};
};
};**
or rewrite by not using push_back (since you know all sizes)
std::vector<vector<float>> electron(n+1);
// std::vector<float> angle;
**randutils::mt19937_rng rng2;
std::vector<float> rand_scatter(n+1);
for (int i = 0; i <= n; i++)
{
std::vector<float>& w=electron[i];
w.reserve(2000+1);
float r=rng2.uniform(0.0, 1.0);
rand_scatter[i]=r;
for (int j = 0; j <= 2000; j++)
{
float f;
if (e_scatter[i] == 0)
{
f=linspace[j] * (cos((r * 90) * (PI / 180)));
// f=abs(f);
}
else
{
f=linspace[j];
};
w[j]=f;
};
};**
After that runtime might decrease to at most few seconds.
Another optimization
string fileName_escatter = "escatter.dat";
FILE* dout4 = fopen(fileName_escatter.c_str(), "w");
for (int i = 0; i <= n; i++)
{
fprintf(dout4, "%d\n", e_scatter[i]); // save one method call
// fprintf(dout2, "%f\n", e_scatter[i]);
};
fclose(dout4);
BTW: ofstream is the stl-way of writing files, like
ofstream dout4("escatter.dat", std::ofstream::out);
for (int i = 0; i <= n; i++)
{
dout4 << e_scatter[i] << std::endl;
};
dout4.close();