Question

Using C, use mmap() to map a file to memory, and then search through it.

For example, get and print out the first character of each line in the file:

abc

def

ghi

Answer 1

Hi,

mmap as a way of mapping physical memory to address space. But mmap is known for its ability to map files to the address space also.

Here is the code for above-mentioned question. I commented in between for better understanding.

#include <stdio.h>

#include <sys/mman.h>

#include <unistd.h>

#include <fcntl.h>

#include <string.h>

int main(void) {
int fd = open("words", O_RDONLY);
size_t pagesize = getpagesize();

//mapping the file named words to the memory using mmap
char * region = mmap(
    (void * )(pagesize * (1 << 20)), pagesize,
    PROT_READ, MAP_FILE | MAP_PRIVATE,
    fd, 0
);

//printing first charecter

if ( * region != '\0') {

printf("%c", * region++);

}

//loop to print first charecter of every line
while ( * region != '\0') {
    if ( * region == '\n') {
      printf("\n%c", *++region);
    }
    * region++;
}
//fwrite(region, 1, pagesize, stdout);
int unmap_result = munmap(region, pagesize);
close(fd);
return 0;
}