How can I read a file with mmap in C?
Yesterday I introduced mmap as a way to map physical memory into the address space. But mmap is more well-known for its ability to map files into the address space.
Here’s an example of reading the system dictionary file by memory-mapping it.
#include <stdio.h>
#include <sys/mman.h>
#include <unistd.h>
#include <fcntl.h>
int main(void) {
int fd = open("/usr/share/dict/words", O_RDONLY);
size_t pagesize = getpagesize();
char * region = mmap(
(void*) (pagesize * (1 << 20)), pagesize,
PROT_READ, MAP_FILE|MAP_PRIVATE,
fd, 0
);
fwrite(region, 1, pagesize, stdout);
int unmap_result = munmap(region, pagesize);
close(fd);
return 0;
}
Tagged . All content copyright James Fisher 2017. This post is not associated with my employer.
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