C++ create a variable number of arrays

Question

I have read columns from a .txt file (the file has at the beginning the number of columns (nCol)) and put the values into an array (float values[nCol][nLin]).

Now, I want to copy the values (ex.: values[0][nLin], values[1][nLin]...) into different float arrays depending on the number of columns.

How can I crate float arrays for each column if the number of columns my change depending on the file I am reading?

//------ Declares Array for values ------//
const int nCol = countCols;
float values[nCol][nLin];

// Fill Array with '-1'
for(int c=0; c<nCol; c++){
    for(int l=0; l<nLin; l++) {
        values[c][l] = -1;
    }
}


//------ Skips the reading of line of values file ------//
getline(inFile, dummyLine);

// reads file to end of *file*, not line 
while(!inFile.eof()) {
    for(int y=0; y<nLin; y++){
        for (int i=0; i<nCol; i++) {
            inFile >> values[i][y];
        }
    i=0;    
    }
}

const int nValues = countLines;

float Col1[nValues]=-1,
      Col2[nValues]=-1,
      Col3[nValues]=-1,
      Col4[nValues]=-1,
      Col5[nValues]=-1;

//------ Put values in specific Arrays ------//

for(int v=0; v<nValues; v++) {
        Col1[v] = values[0][v];
        Col2[v] = values[1][v];
        Col3[v] = values[2][v];
        Col4[v] = values[3][v];
        Col5[v] = values[4][v];
}
cout << endl;

I want that float Col1[] to be from 1 to nCol, the last one to be float ColnCol[]

Abhishek Bansal · Accepted Answer · 2013-12-07 17:49:18Z

3

The best way IMO would be to use std::vector< std::vector<float> >

You do not need to make different 1D columns as you can manipulate this vector of vector as you want.

edited Dec 7, 2013 at 17:49

answered Dec 7, 2013 at 17:43

Abhishek Bansal

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5 Comments

JMG Over a year ago

But is it possible with arrays? I have made the rest of the program and calculations with arrays

Abhishek Bansal Over a year ago

I don't think your program will need to change much since vectors work almost same as arrays (ofcourse with a lot more functionality). And to answer your question, if the number of lines is dynamic, then fixed length arrays cannot be used.

JMG Over a year ago

Sorry to ask, but can you give an example of how could I do it with vectors?

Abhishek Bansal Over a year ago

Instead of Col1[k], use values[0][k] everywhere.

JMG Over a year ago

I'm going to try it. Thank you

Hemerson Tacon · Accepted Answer · 2018-10-17 17:50:06Z

0

Instead you should use std::vector. It is a better choice for dynamic size allocation of a data type.

edited Oct 17, 2018 at 17:50

Hemerson Tacon

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answered Oct 17, 2018 at 17:13

Vaibhav Choudhary

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