#include <stdio.h>
#include <string.h>

struct pseudo_header
{
    int var1;
    int var2;
    char name[25];
};

void csum(const unsigned short* ptr, int nbytes)
{

    unsigned long sum = 0;

    for(int i = 0; i < sizeof(struct pseudo_header); i++)
    {
        sum+= ptr[i];
    }

    printf("%lu", sum);
}

int main() {

    struct pseudo_header psh;
    char datagram[4096];

    psh.var1 = 10;
    psh.var2 = 20;

    strcpy(psh.name, "test");
    memcpy(datagram, &psh, sizeof(struct pseudo_header));

    csum((unsigned  short*)datagram, sizeof(struct pseudo_header));

    return 0;
}