C Language Structs Passing structs to functions
Example
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;
}
