mmap

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <vector>

bool die(const char *s)
{
    perror(s);
    exit(1);
}
int main(int argc,char **argv)
{
    char c;
    int num=0;
    int pos=1;
    int line=1;

    std::vector<int> res;

    struct stat statbuf;
    int fd=open(argv[1],O_RDONLY);
    (fd>0) || die("open");
    (fstat(fd,&statbuf)==0) || die("stat");

    void *mem=mmap(0,statbuf.st_size,PROT_READ,MAP_SHARED,fd,0);
    mem || die("mmap");
    char *head=(char*)mem;
    char *tail=head+statbuf.st_size;
    while((c=*head++),(head<=tail))
    {
        if (c>='0' && c<='9')
            num=num*10+c-'0';
        else if (c=='-') pos=0;
        else if (c=='\n')
        {
            num=pos?num:-num;
            res.push_back(num);
            num=0;
            pos=1;
            line++;
        }
        else
        {
            printf("I've got a problem with this file at line %d\n",line);
            exit(1);
        }
    }
    unsigned sum=0;
    for (int i=0;i<res.size();i++)
    {
        sum=sum+(unsigned)res[i];
    }
    printf("=>%d\n",sum);
}