C语言学习

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

#define SEARCH_WORD "like"

int main(int argc, char *argv[])
{
    size_t page = (size_t)sysconf(_SC_PAGESIZE);
    printf("page size is %ld.\n", page);

    int fd = open("./mmap.manual", O_RDONLY);
    struct stat st; 
    fstat(fd, &st);

    off_t offset = 0;
    off_t aligned = offset & ~(page - 1); 
    /* offset for mmap() must be page aligned */

    size_t length = st.st_size - offset;

    void *addr = mmap(NULL, length + offset - aligned, PROT_READ,
            MAP_PRIVATE, fd, aligned);
    if (addr == MAP_FAILED) {
        perror("mmap");
        exit(EXIT_FAILURE);
    }   

    int n = 0;
    char *word = strstr(addr + offset - aligned, SEARCH_WORD);
    while (word) {
        n++;
        word = strstr(word + strlen(SEARCH_WORD), SEARCH_WORD);
    }   
    printf("there are %d `%s` word.\n", n, SEARCH_WORD);

    close(fd);
    munmap(addr, length);
    exit(EXIT_SUCCESS);
}