Reputation: 1421
typedef struct { double x, y; } vec;
typedef struct { int n; vec* v; } polygon_t, *polygon;
#define BIN_V(op, xx, yy) vec v##op(vec a, vec b) { \
vec c; c.x = xx; c.y = yy; return c; }
#define BIN_S(op, r) double v##op(vec a, vec b) { return r; }
BIN_V(sub, a.x - b.x, a.y - b.y);
BIN_V(add, a.x + b.x, a.y + b.y);
BIN_S(dot, a.x * b.x + a.y * b.y);
BIN_S(cross, a.x * b.y - a.y * b.x);
vec testPoints[] = {
{1, 1},
{3, 3},
{3, 5},
{5, 2},
{6, 3},
{7, 4}
};
What does the array of structs at last work? I don't quite understand how {1, 1}
become a vec.
If I want to have a vector<vec> allPoints
, how can I push a vec into this vector? This doesn't work allPoints.push_back({1, 2});
, as well as allPoints.push_back(new vec(1, 2));
Upvotes: 2
Views: 2410
Reputation: 154025
Constructing C-like structs on the fly doesn't work in C++2003. It works in C++2011:
std::vector<vec> v;
v.push_back(vec{ 1, 2 });
If you need to create a std::vector<vec>
in C++2003 the best way is probably to create a helper function to initialize your objects
vec make_vec(double a, double b) {
vec v = { a, b };
return v;
}
...
v.push_back(make_vec(1, 2));
Upvotes: 2
Reputation: 122001
The {}
is an initializer and:
vec v = { 2, 3 };
is equivalent to:
vec v;
v.x = 2;
v.y = 4;
For an array:
int myints[3] = { 1, 2, 3 };
would initialise the elements in the array:
myints[0] = 1;
myints[1] = 2;
myints[2] = 3;
For an array of structs:
vec mystructs[2] = { { 1, 2}, { 2, 3} };
initialises the array of structs:
mystructs[0].x = 1;
mystructs[0].y = 2;
mystructs[1].x = 2;
mystructs[1].y = 3;
To use a std::vector<vec>
in the manner you expressed add a constructor to the vec
struct:
struct vec
{
vec(double a_x, double a_y) : x(a_x), y(a_y) {}
double x,y;
};
std::vector<vec> allPoints;
allPoints.push_back(vec(1,2));
Upvotes: 4