Large arrays using preprocessor directives in C

Question

Is the following a valid syntax? If yes, the please explain how it works .

double array[SIZE][SIZE] = {
    #include "float_values.txt"
}

Answer 1

Yes, this is valid C syntax.

In C and C++, #include directives are very simple: they just copy and paste the contents of the file you're using into the current file, replacing the #include directive.

For example, if your "float_values.txt" file looked like this:

{1.0, 2.0},
{3.0, 4.0}

Then the preprocessor would transform your code to look like this:

double array[SIZE][SIZE] = {
    {1.0, 2.0},
    {3.0, 4.0} 
}

However, you must ensure SIZE is defined correctly.

Answer 2

Yes, this code snippet is valid.

The preprocessor will find the #include directive and search for a file named float_values.txt within the given search paths. Then the contents of that file will be taken and #include "float_values.txt" will be replaced with the contents of the file. If the resulting code is valid purely depends on the content of the file. To be valid, the file must contain data to initialize a two dimensional array of doubles, but must not contain more values than permitted by the value of SIZE. Less values would be okay as the remaining doubles would be default initialized.