/*
* This copies files by memory mapping them. This is to demonstrate memory
* mapping, rather than because this it's a wonderful way to do this.
*/
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#define BUF_SIZE 1024
/* Error and die. */
void croak(char *msg, int syserr)
{
fprintf(stderr, "%s", msg);
if(syserr) fprintf(stderr, ": %s", strerror(errno));
fprintf(stderr, "\n");
exit(1);
}
int main(int argc, char **argv)
{
int infile, outfile; /* Input and output file descrs. */
int flen, m; /* File length. */
char *inloc, *outloc; /* Mapped locations. */
char *inscan, *outscan; /* Memory scanning pointers. */
if(argc != 3) croak("Need three args.", 0);
/* Open the input file to read. */
infile = open(argv[1], O_RDONLY);
if(infile < 0) croak("Input file open", 1);
/* Find the lenth of the file by seeking to the end. */
flen = lseek(infile, 0, SEEK_END);
if(flen < 0) croak("Input seek to end", 1);
/* Open output file, writable, truncate existing content, or create
if not. */
outfile = open(argv[2], O_RDWR | O_CREAT, 0777);
if(outfile < 0) croak("Output file open", 1);
/* Set the size of the output file to the size of the input file. If
it's larger, the extra will be removed. If smaller, it's filled
with zero bytes. */
if(ftruncate(outfile, flen) < 0) croak("Output size set", 1);
/* Map the files into virtual memory. */
inloc = mmap(NULL, flen, PROT_READ, MAP_SHARED, infile, 0);
if(outloc == (void *) -1) croak("Input map", 1);
outloc = mmap(NULL, flen, PROT_WRITE, MAP_SHARED, outfile, 0);
if(outloc == (void *) -1) croak("Output map", 1);
/* Copy the file by copying the memory regions. */
inscan = inloc;
outscan = outloc;
for(m = flen; m--;) *outscan++ = *inscan++;
/* Clean up this mess. */
munmap(inloc, flen);
munmap(outloc, flen);
close(infile);
close(outfile);
}