使用read, write, scanf, printf等系统调用或库函数，可以实现简单的文件复制程序，但效率上有明显差别。
方法一：逐个字符读入并输出
#include <stdio.h> #include <unistd.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <stdlib.h> int main(void){ char c; int in, out; in=open("file.in", O_RDONLY); out=open("file.out", O_WRONLY|O_CREAT, S_IRUSR|S_IWUSR); while(read(in, &c, 1)==1){ write(out, &c, 1); } exit(0); }执行效率：
[lujinhong@lujinhong BeginningLinuxProgramming]$ TIMEFORAMT="" time ./a.out 0.31user 8.07system 0:08.40elapsed 99%CPU (0avgtext+0avgdata 1392maxresident)k 0inputs+9032outputs (0major+110minor)pagefaults 0swaps
方法二：每次读入1K再输出
#include <stdio.h> #include <unistd.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <stdlib.h> #define READ_SIZE 1024 int main(void){ char c[READ_SIZE]; int in, out; int nread; in=open("file.in", O_RDONLY); out=open("file.out", O_WRONLY|O_CREAT, S_IRUSR|S_IWUSR); while((nread=read(in, c, READ_SIZE))>0){ write(out, c, nread); } exit(0); }执行效率：
[lujinhong@lujinhong BeginningLinuxProgramming]$ TIMEFORAMT="" time ./a.out 0.00user 0.01system 0:00.01elapsed 92%CPU (0avgtext+0avgdata 1408maxresident)k 0inputs+9032outputs (0major+111minor)pagefaults 0swaps
转载于:https://www.cnblogs.com/jinhong-lu/archive/2013/02/17/4559556.html
