Table of contents
system call
The program setting is 10, so the program runs at a maximum of 10, which is particularly time-consuming when writing large files. Because the program writes data directly into the kernel from buf , this process is the most time-consuming, and then needs to return from the kernel to buf .
the code
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <stdlib.h>
int main(int argc,char *argv[]){
char buf[1024];
int n=0;
int fp1=open(argv[1],O_RDONLY);
if(fp1==-1){
perror("fp1 error");
exit(1);
}
int fp2=open(argv[2],O_RDWR|O_CREAT|O_TRUNC,0664);
if(fp2==-1){
perror("fp2 error");
exit(1);
}
while((n=read(fp1,buf,10))!=0){
if(n<0){
perror("read error");
break;
}
write(fp2,buf,n);
}
close(fp1);
close(fp2);
return 0;
}Library Functions
The library function is written 4096 at a time. First store the data of buf in the blue buffer area , store 4096 bytes and then write it into the kernel at one time , so in some cases, library functions are better than system calls.
the code
#include <stdio.h>
#include <stdlib.h>
int main(void){
FILE *fp,*fp_out;
int n;
fp = fopen("a1.txt","r");
if(fp == NULL){
perror("fopen error");
exit(1);
}
fp_out = fopen("a3.txt","w" );
if(fp_out == NULL){
perror("fopen error");
exit(1);
}
while((n = fgetc(fp)) != EOF){
fputc(n,fp_out);
}
fclose(fp);
fclose(fp_out);
return 0;
}