In solidity the structs given as parameters for a function are mostly given by value, meaning that the whole struct is practically duplicated in memory and handled as a local copy of the original struct. There is one exception that you can use if you want to use another semantics: with internal and private functions you can use the storage keyword to make sure that the struct us handled as reference and not as value.
contract StructTestContract {
struct TestStruct{
uint a;
}
TestStruct public myStruct= TestStruct(1);
function copyStructByValue(TestStruct _struct){
_struct.a = 2;
}
function copyStructByReference(TestStruct storage _struct) internal{
_struct.a = 2;
}
function testCopyStructByValue(){
copyStructByValue(myStruct);
}
function testCopyStructByReference(){
copyStructByReference(myStruct);
}
}
In the previous example, copyStructByReference has got a real reference to the TestStruct resulting 2 after the function call, as copyStructByValue simply copies the whole struct meaning that the original value will not change.
