What you mean by row major and column major?

Answer 1

its the method for sorting the multidimensional array.

eg:

consider the matrix: 10 1 3

2 7 5

8 6 4

row-major order: 1 3 10

2 5 7

4 6 8

column major order: 2 1 3

8 6 4

10 7 5

Answer 2

Row-major and column-major describe the two ways in which a multi-dimensional array can be laid out in memory. Array layout is critical when passing arrays between two programs written in different languages because every programming language has its own "native" array layout:

Row-major languages include:

• C/C++/Objective-C (for all C-style arrays)
• C#/CLI/.Net
• Mathematica
• Pascal
• PL/I
• Speakeasy
• SAS

Column-major languages include:

• Fortran
• OpenGL and OpenGL ES
• MATLAB
• Gnu-Octave
• S-Plus
• R
• Julia
• Scilab

We cannot change the native layout of a language, however we can switch from one memory layout to another simply by transposing the array dimensions.

Consider the following array:

1 2 3 4

5 6 7 8

In C (a row-major language), we would declare this array as follows:

int x[2][4] = {{1, 2, 3, 4}, {5, 6, 7, 8}};

Once initialised, the elements will be laid out in contiguous memory addresses as follows:

1 2 3 4 5 6 7 8

We call this row-major because the elements are grouped by row:

{1, 2, 3, 4}, {5, 6, 7, 8}

In a column-major programming language, the same array would be laid out as follows:

1 5 2 6 3 7 4 8

Here, the elements are grouped by column:

{1, 5}, {2, 6}, {3, 7}, {4, 8}

To transform our row-major array into a column-major array we simply transpose the array:

int y[4][2]; // transposed array

for (row=0; row<2; ++row)

for (col=0; col<4; ++col)

y[col][row]=x[row][col];

Once executed, the memory layouts of x and y are as follows:

x = 1 2 3 4 5 6 7 8

y = 1 5 2 6 3 7 4 8

Note that y is not a column-major array (it is a row-major array because the language is row-major) however the memory layout is the layout expected of a column-major language.