passing struct array as parameter to a function

Question

I am trying to set a array of structure in a array of structure. to this i have created a function. how ever i try it i am not able to do it.

struct polygon {
struct point polygonVertexes[100];
};
struct polygon polygons[800];
int polygonCounter = 0;


int setPolygonQuardinates(struct point polygonVertexes[]) {
    memcpy(polygons[polygonCounter].polygonVertexes, polygonVertexes,4);
}

int main(){

    struct point polygonPoints[100] = {points[point1], points[point2], points[point3], points[point4]};

    setPolygonQuardinates(polygonPoints);
    drawpolygon();
}



void drawpolygon() {
    for (int i = 0; polygons[i].polygonVertexes != NULL; i++) {
        glBegin(GL_POLYGON);
        for (int j= 0; polygons[i].polygonVertexes[j].x != NULL; j++)    {
            struct point pointToDraw = {polygons[i].polygonVertexes[j].x, polygons[i].polygonVertexes[j].y};
            glVertex2i(pointToDraw.x, pointToDraw.y);
        }
        glEnd();
    }
}

when i run this i get the following error

Segmentation fault; core dumped; real time

sorry for the bad English. what i meant was that i am not able to copy the polygonPoints array into the polygonVertexes member of polygon structure. After the setPolygonQuardinates function executes the polygonVertexes member has junk values. — Naseeruddin V N, Apr 22 '17 at 14:57
@GauravPathak i have edit and added the information. please review and comment your observation. — Naseeruddin V N, Apr 22 '17 at 15:11
What's `strcpy` doing in this code? I don't see a single string in it. What is `strcpy(polygons[polygonCounter].polygonVertexes, polygonVertexes)` even supposed to do? — AnT stands with Russia, Apr 22 '17 at 15:12
Why are you using 'strcpy' instead of 'memcpy'? It seems to me that you should use memcpy with type being your polygon. — user3002166, Apr 22 '17 at 15:14
@AnT i tried with `polygons[polygonCounter].polygonVertexes = polygonVertexes` and that didnt work so i used that after searching on stackoverflow. — Naseeruddin V N, Apr 22 '17 at 15:15
@Naseeruddin V N: You tried to do *what* exactly? Either version makes no sense. What are you trying to achieve? — AnT stands with Russia, Apr 22 '17 at 15:17
@AnT with setPolygonQuardinates() function i am trying to set the polygonVertexes array in the polygon struct's polygonVertexes member. please let tell me if find anything wrong with it. — Naseeruddin V N, Apr 22 '17 at 15:24

score 0 · Accepted Answer · 2017-04-22T15:54:03.960

0

You cannot use strcpy here; that is for null-terminated strings. A struct is not a null-terminated string :) To copy objects around, use memcpy.

To pass arrays around in C, a second parameter stating the number of objects in the array is usually passed as well. Alternatively, the array and length are put into a struct, and that struct is passed around.

EDIT: An example of how to do this:

void setPolygonQuardinates(struct point* polygonVertexes, size_t polygonVertexesSize) {
    memcpy(polygons[polygonCounter].polygonVertexes, polygonVertexes, sizeof(point) * polygonVertexesSize);
}

int main(){
    struct point polygonPoints[100] = {points[point1], points[point2], points[point3], points[point4]};
                         /*     ^---------v   make sure they match */
    setPolygonQuardinates(polygonPoints, 100);
    drawpolygon();
}

If you need this explained, please ask. I think it is idiomatic C code.

edited Apr 22 '17 at 15:54

answered Apr 22 '17 at 15:14

i tried this but im still getting the same error. what else can i do to store the points array in the structure member array – Naseeruddin V N Apr 22 '17 at 15:35
thanks a lot for the help, That solved my problem. I am still learning to code and would love to know how to code better. – Naseeruddin V N Apr 22 '17 at 16:19
@NaseeruddinVN To do anything better you gotta keep practicing! Remember, all the experts here were beginners once. – Apr 22 '17 at 16:22

passing struct array as parameter to a function

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