#include<stdlib.h>
#include<stdio.h>
#include<string.h>
#include<sys/mman.h>
#include<sys/stat.h>
#include<unistd.h>
#include<fcntl.h>
#define FILE_LENGTH 10000

int main(int argc,char *argv[])
{
	if(argc!=2)
    {
        printf("Usage: %s filename\n",argv[0]);
        return 0;
    }
	int fd,count=0;
	char *map_memory,*ca;
	
	fd = open(argv[1], O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
	
	lseek(fd, FILE_LENGTH+1, SEEK_SET);
	write(fd, "", 1);
	lseek(fd, 0, SEEK_SET);
	map_memory =(char*) mmap(0, FILE_LENGTH, PROT_WRITE, MAP_SHARED, fd, 0);
	close(fd);
	
	ca = map_memory;
	while( FILE_LENGTH>count && fgets(ca,FILE_LENGTH-count,stdin)!=NULL )
	{
		int tmp = strlen(ca);
		count += tmp;
		ca += tmp;
	}
	
	munmap(map_memory, FILE_LENGTH);
	return 0;
}

 

#include<stdlib.h>
#include<stdio.h>
#include<string.h>
#include<sys/mman.h>
#include<sys/stat.h>
#include<unistd.h>
#include<fcntl.h>
#define FILE_LENGTH 10000

int main(int argc,char *argv[])
{
	if(argc!=4)
    {
        printf("Usage: %s filename start_pos end_pos\n",argv[0]);
        return 1;
    }
	int start_pos=0, end_pos=0;
	start_pos = atoi(argv[2]);
	end_pos = atoi(argv[3]);
	if(start_pos<0 || end_pos>FILE_LENGTH || start_pos>end_pos)
	{
		puts("start_pos or end_pos error. Please try again.");
        return 1;
	}
	int fd,i;
	char *map_memory;
	
	fd = open(argv[1], O_RDWR | O_CREAT, S_IRUSR | S_IWUSR);
	
	lseek(fd, FILE_LENGTH+1, SEEK_SET);
	write(fd, "", 1);
	lseek(fd, 0, SEEK_SET);
	map_memory =(char*) mmap(0, FILE_LENGTH, PROT_WRITE, MAP_SHARED, fd, 0);
	close(fd);
	
	printf("Substring from [%d] to [%d] is: ",start_pos,end_pos);
	for(i=start_pos-1;i<end_pos;i++)
		printf("%c",*(map_memory+i));
	puts("");
	
	munmap(map_memory, FILE_LENGTH);
	return 0;
}
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