Passing structs to functions

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In C, all arguments are passed to functions by value, including structs. For small structs, this is a good thing as it means there is no overhead from accessing the data through a pointer. However, it also makes it very easy to accidentally pass a huge struct resulting in poor performance, particularly if the programmer is used to other languages where arguments are passed by reference.

struct coordinates
    int x;
    int y;
    int z;

// Passing and returning a small struct by value, very fast
struct coordinates move(struct coordinates position, struct coordinates movement)
    position.x += movement.x;
    position.y += movement.y;
    position.z += movement.z;
    return position;

// A very big struct
struct lotsOfData
    int param1;
    char param2[80000];

// Passing and returning a large struct by value, very slow!
// Given the large size of the struct this could even cause stack overflow
struct lotsOfData doubleParam1(struct lotsOfData value)
    value.param1 *= 2;
    return value;

// Passing the large struct by pointer instead, fairly fast
void doubleParam1ByPtr(struct lotsOfData *value)
    value->param1 *= 2;

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