内存映射文件mmap demo

#include <stdio.h>

#include <stdlib.h>

#include <fcntl.h>

#include <unistd.h>

#include <sys/types.h>

#include <sys/mman.h>

#include <sys/stat.h>

#include <errno.h>

#define TEST_FILE "00000.txt"

int main(int argc, char *argv[])

{

int fd, offset;

char *data;

struct stat sbuf;

if (argc != 2) {

fprintf(stderr, "usage: test offset\n");

exit(1);

}

fd = open(TEST_FILE, O_CREAT | O_RDWR);

if(fd < 0){

perror("open");

return -1;

}

char *s = "xuzhh1";

if(write(fd, s, strlen(s)) < 0){

perror("fwrite");

}

if (stat(TEST_FILE, &sbuf) == -1) {

perror("stat");

exit(1);

}

offset = atoi(argv[1]);

if (offset < 0 || offset >sbuf.st_size-1) {

fprintf(stderr, "mmapdemo: offset must be in the range0-%lu\n", sbuf.st_size-1);

exit(1);

}

if ((data = mmap((caddr_t)0, sbuf.st_size, PROT_WRITE |PROT_READ, MAP_SHARED, fd, 0)) == (caddr_t)(-1)) {

perror("mmap");

exit(1);

}

printf("byte at offset %d is '%c'\n", offset,data[offset]);

data[1] = '0';

memset(data, 0x0, sbuf.st_size);

strncpy(data, "this is very, useful\n", strlen("this is very,useful\n"));

munmap(data, sbuf.st_size);

close(fd);

return 0;

}