将结构传递给函数

Question

When you pass a struct to a function, is it pass by value (similar to regular variables where the value gets cloned), or is it pass by reference (similar to arrays where the actual variable is passed)? Can you give an example.

Answer 1

In C everything is pass by value, even passing pointers is pass by value. And you never can change the actual parameter's value(s).

That is from K&R by the way. And I recommend to read that book. Saves you many questions you might post in the future.

Answer 2

A struct is passed by value:

struct S {
    int a,b; 
};

void f(struct S s) {
    printf("%d\n", s.a+s.b); 
    s.a = 0;   /* change of a in local copy of struct  */
}

int main(void) {
    struct S x = { 12,13};
    f(x);
    printf ("Unchanged a: %d\n",x.a);
    return 0;
}

Online demo

Answer 3

You are passing it by value. Everything in a structure is copied.