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POGlobal variables and Return multiple variable length arrays (pointers) in C function
 

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    <p>I have some programming experience but not much with C.</p> <p>I have a reasonably large C file. In it there are multiple functions that are executed sequentially - so in this particular case no function is called twice really, they are broken down for ease of reading, since each function still has a separate purpose.</p> <p>This program does a lot of computations on several long arrays of double with variable length, so they are all pointers. Two questions:</p> <p>1) The variables that are calculated once from the beginning and then serve as input to many subsequent functions - should I make them global variables inside this file? From my experience programming in higher level languages, global variables are not good. Is this not the case for C and why?</p> <p>2) When 1 of my function wants to return multiple pointers (each points to an double array of length n for example), say double *p1, double *p2, double *p3 that are related, I can combine them into a struct:</p> <pre><code>struct pointers { double *p1, *p2, *p3; } ptr; </code></pre> <p>foo1 will take double *input as input, and calculate ptr->p1, ptr->p2, ptr->p3, and then ptr will later serve as input for foo2. Should I write </p> <pre><code>struct pointers *foo(double *input) </code></pre> <p>or</p> <pre><code>void foo1(double *input, struct pointers ptr) </code></pre> <p>or</p> <pre><code>void foo1(double *input, struct pointers *ptr) </code></pre> <p>Why is it that C functions are usually 'void' functions, unless it returns just an int or double variables? Having input and output both as parameters - is it confusing?</p> <p>Should I initialize ptr->p1, ptr->p2, ptr->p3 inside or outside of foo1? </p> <p>Note that foo() is the main function that will call foo1, foo2 sequentially.</p>
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