Writing a 2D array to a file

[mickey22]

I have a 2D array a[336][336] and I wanted to write this array into a text file.

I have created a 2d pointer but I am not able to understand how to make this pointer point to this array. Could anyone please help me with this? Thanks in advance.

Here’s the part of the code that I have written.

float a[336][336];
FILE *qfile;
qfile=fopen("D:/c.txt","wb");
float **img;
img=new float*[336];
for(unsigned long int i=0;i<336;i++)
{
 
*(img+ i) = new float[336];
}
 
for (unsigned long int i = 0; i < 336; i++)
{
 fwrite(*(img + i), 4, 336, qfile);
}
fclose(qfile);

[horace1]

is there any reason why you can do this

FILE *qfile;
qfile=fopen("D:/c.txt","wb");
int i;
 
for(i=0;i<336;i++)
{
 fwrite(a[i], sizeof(float), 336, qfile);
}
fclose(qfile);

[mickey22]

I was trying to use pointer but I did not know I can just do it so simple.It worked and thank you so much for your help.

[weaknessforcats]

A couple of things here:

float **img;

is not a 2D pointer. A float** is a pointer to a pointer to a single float.

This array:

float a[336][336];

is an array of 336 elements where each element is itselt and array of 336 floats. Following the rule that the name of the array is the address of element 0, you need a pointer to an array of 336 floats:

float (*ptr)[336] = a;

Here ptr is such a 2D pointer and can point to the array "a".

However, all array elements are contiguous in memory so the 336 floats for
a[0] precede the 336 floats of a[1]. This is done so pointer arithmetic works in locating an element of the array. That makes the memory layout of a 2D array [336][336] exactly the same as a 1D array of [336 * 336].

Following that, just write out 336 * 336 floats:

float* ptr;

ptr = &a[0][0];

fwrite(ptr, sizeof(float), 336 * 336, qfile);

fclose(qfile);