What does this line mean?, can we assign something to an object other than attribute?-CodePudding

Greetings this is my first question here.

I'm really new to C , and to Object Oriented Programming as well.

So, my tasks currently need to wrap this C library, the code is:

#include "cavc/polylineoffset.hpp"

int main(int argc, char *argv[]) {
    (void)argc;
    (void)argv;
    // input polyline
    cavc::Polyline<double> input;
    // add vertexes as (x, y, bulge)
    input.addVertex(0, 25, 1);
    input.addVertex(0, 0, 0);
    input.addVertex(2, 0, 1);
    input.addVertex(10, 0, -0.5);
    input.addVertex(8, 9, 0.374794619217547);
    input.addVertex(21, 0, 0);
    input.addVertex(23, 0, 1);
    input.addVertex(32, 0, -0.5);
    input.addVertex(28, 0, 0.5);
    input.addVertex(39, 21, 0);
    input.addVertex(28, 12, 0);
    input.isClosed() = true;

    // below this is the line that i dont understand
    std::vector<cavc::Polyline<double>> results = cavc::parallelOffset(input, 3.0);
}

So, what I don't understand is the last line. The basic C OOP that I understand is that we can create an object and can assign an attribute to it:

class MyClass {       // The class
    public:             // Access specifier
    int myNum;        // Attribute (int variable)
    string myString;  // Attribute (string variable)
};

myClass myObject;
myObject.myNum = 1;
myObject.myString = "something";

But, what I don't understand in the last line (from the library) is it's creating an object from a class which is results but after that, directly assign to something:

results = cavc::parallelOffset(input, 3.0);

This is the header file:

https://github.com/jbuckmccready/CavalierContours/blob/master/include/cavc/polylineoffset.hpp

CodePudding user response：

The line in question is calling a function named parallelOffset, that was declared in a namespace called cavc. The function returns an object of type std::vector<cavc::Polyline<double>>, so the line is declaring an object of that type and setting it equal to the value retuned by the function.

The syntax is the same as e.g.

float x = sin(3.0);

... just with a more complicated return-type (std::vector<cavc::Polyline<double>>, a.k.a a vector of cavc::Polyline<double> objects)

std::vector<cavc::Polyline<double>> results = cavc::parallelOffset(input, 3.0);