Using Custom Vectors in C - c

Question

I'm fairly new to C/C++, but I'm trying to debug some code. It uses a vector that someone had called CART8 and is structured as such:
typedef struct crt8 {
double x;
double y;
double z; } CART8;
Now my question is this. How do I create and populate an instance of an vector of type CART8 called vector1? I've read through a lot of material, and even found a site that indicate how you would create the vector...as indicated above, but no information on HOW to actually use it.

Answer 1

typedef is used extensively in C to refer to struct variables without specifying the struct prefix, for example if I had:
struct vector {
double x;
double y;
double z;
};
than to initialize it I'd have to do:
struct vector vector1;
vector1.x = 1.11;
vector1.y = 1.22;
vector1.z = 1.33;
But if I used a typedef in the declaration:
typedef struct vector {
double x;
double y;
double z;
} vector_type;
than I could simplify this initialization like so (note the struct prefix is not needed now):
vector_type vector1;
vector1.x = 1.11;
vector1.y = 1.22;
vector1.z = 1.33;
Of course, I could still use the full struct vector initialization in this case as well
So in your case:
#include <stdio.h>
typedef struct crt8 {
double x;
double y;
double z;
} CART8;
int main(int argc, char** argv)
{
CART8 vector1;
vector1.x = 2.526;
vector1.y = 3.416;
vector1.z = 4.32;
printf("%f %f %f\n", vector1.x, vector1.y, vector1.z);
}
Alternatively, you can always resort to the original struct definition:
#include <stdio.h>
typedef struct crt8 {
double x;
double y;
double z;
} CART8;
int main(int argc, char** argv)
{
struct crt8 x;
x.x = 2.341;
x.y = 3.43;
x.z = 4.521;
printf("%f %f %f\n", x.x, x.y, x.z);
}

Answer 2

You wrote:
typedef struct crt8 {
double x;
double y;
double z;
} CART8;
This defined a new 'type'. The 'typename' is struct crt8 or the alias you defined CART8. This is how you instantiate an object from that type in C:
struct crt8 myVector;
or you can use the alias 'CART8' that you've defined:
CART8 myVector;
Either way, this is how you populate the 'members' of your object:
CART8 x; // Creation of object
x.x = 100;
x.y = 101;
x.z = 102;

Answer 3

Here is a demonstrative program that shows various ways how objects of the structure can be created, initialized, and used.
#include <stdio.h>
#include <math.h>
typedef struct crt8 {
double x;
double y;
double z; } CART8;
int main( void )
{
CART8 vector1 = { 1.1, 2.2, 3.3 };
CART8 vector2 = { .x = 1.1, .y = 2.2, .z = 3.3 };
CART8 vector3;
vector3.x = 1.1;
vector3.y = 2.2;
vector3.z = 3.3;
CART8 vector4 = vector1;
CART8 vector5 = { vector1.x + vector2.z, vector1.y + vector2.y, vector1.z + vector2.x };
printf( "vector5 = { %lf, %lf, %lf }\n", vector5.x, vector5.y, vector5.z );
printf( "Magnitude = %lf", sqrt( pow( vector1.x, 2 ) + pow( vector1.y, 2 ) + pow( vector1.z, 2 ) ) );
return 0;
}
The output is
vector5 = { 4.400000, 4.400000, 4.400000 }
Magnitude = 4.115823