Structures and functions in C

Question

I am getting errors in the following code. The errors disappear if I take out "struct point p2...". p1 is assembled the same way and works fine, what is the catch here?

#include <stdio.h>

struct point {
    int x;
    int y;
};

struct point makepoint(int x, int y)
{
    struct point temp;

    temp.x = x;
    temp.y = y;
    return temp;
}
struct point addpoint(struct point p1, struct point p2)
{
    p1.x += p2.x;
    p1.y += p2.y;
    return p1;
}

void main()
{
    struct point p1 = makepoint(5, 7);
    printf("p1 = (%d, %d)\n", p1.x, p1.y);
    struct point p2 = makepoint(2, 9);
    printf("p2 = (%d, %d)\n", p2.x, p2.y);
}

Answer 1

• To avoid the many hidden calls to memcpy()
• To avoid the many compiler allocated memory areas (that cannot be accessed/used by anything else.)

I suggest the following code, which compiles cleanly and exercises each function

#include <stdio.h>

struct point
{
    int x;
    int y;
};

void makepoint(int x, int y, struct point* newPoint)
{
    newPoint->x = x;
    newPoint->y = y;
} // end function: makepoint

void addpoint(struct point* p1, struct point* p2)
{
    p1->x += p2->x;
    p1->y += p2->y;
} // end function: addpoint

int main()
{
    struct point p1;
    struct point p2;

    makepoint(5, 7, &p1);
    printf("p1 = (%d, %d)\n", p1.x, p1.y);

    makepoint(2, 9, &p2);
    printf("p2 = (%d, %d)\n", p2.x, p2.y);

    addpoint( &p1, &p2 );
    printf("p1 = (%d, %d)\n", p1.x, p1.y);

    return(0);
} // end function: main