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Why is this program so slow? It takes a minute, 34 seconds on my system to copy the file, while the Linux cp command does the same thing in less than half a second. What can be done to make the program faster?
1 /************************************************
2 * copy input file to output file. *
3 ************************************************/
4 #include <iostream>
5 #include <unistd.h>
6 #include <fcntl.h>
7
8 int main() {
9 // The fd of the input file
10 int in_fd = open("file.in", O_RDONLY);
11
12 // The fd of the output file
13 int out_fd = open("file.out",
14 O_WRONLY|O_CREAT, 0666);
15
16 char ch; // Character to copy
17
18 if (in_fd < 0) {
19 std::cout <<
20 "Error could not open input file\n";
21 exit (8);
22 }
23
24 if (out_fd < 0) {
25 std::cout <<
26 "Error could not open output file\n";
27 exit (8);
28 }
29 while (1) {
30 if (read(in_fd, &ch, 1) != 1)
31 break;
32
33 write(out_fd, &ch, 1);
34 }
35 close(in_fd);
36 close(out_fd);
37 return (0);
38 }
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