pass c-array via pipe

.gitignore

#
/echo_vertices

__main__.py

import struct, sys

from subprocess import Popen, PIPE

def pack(vertices, n):    
    yield struct.pack('i', n)
    s = struct.Struct('i f f')
    for v in vertices:
        yield s.pack(*v)

def main():
    try: n = int(sys.argv[1])
    except IndexError:
        n = 100
    vertices = ((i,i+1,i+2) for i in range(n))

    p = Popen(["./echo_vertices", "random", "arg"], stdin=PIPE, stdout=PIPE)
    out, _ = p.communicate(b''.join(pack(vertices, n)))

    index, x, y = struct.unpack('iff', out)
    assert index == (n-1) and int(x) == n and int(y) == (n+1)

if __name__ == '__main__':
    main()

echo_vertices.c

/** http://stackoverflow.com/questions/4979421/subprocess-popen-invalid-argument-broken-pipe-while-comunicating-to-c-program */
#include<stdio.h>
#include<stdlib.h>

typedef struct {
    int index;
    float x;
    float y;
}  vertex;

int main(int argc, char* argv[]) {
    int i;
    vertex* VV;
    int n = 0;
    fread(&n, sizeof(int), 1, stdin);
    VV =(vertex*) malloc(sizeof(vertex)*n);
    fread(VV,sizeof(vertex),n,stdin);

    /* write the last vertex */
    fwrite(&VV[n-1], sizeof(vertex), 1, stdout);
}