Linux---文件操作
Posted qnbk
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文件操作
C语言中的文件读&写
#include <stdio.h>
int main()
{
FILE* fp = fopen("log.txt","r");
if(fp == NULL)
{
perror("fopen");
return 1;
}
int ct = 5;
char buf[64];
while(ct){
fgets(buf,sizeof(buf),fp);
printf(buf);
ct--;
}
/*
int ct = 5;
while(ct)
{
fputs("hello world \\n",fp);
ct--;
}
*/
fclose(fp);
return 0;
}
stdin
标准输入
FILE* fp = fopen("log.txt","r");
if(fp == NULL)
{
perror("fopen");
return 1;
}
int ct = 5;
char buf[64];
while(ct){
fgets(buf,sizeof(buf),stdin);
printf(buf);
ct--;
}
stdout
标准输出
int ct = 5;
while(ct)
{
fputs("hello world \\n",stdout);
ct--;
}
stderr
标准错误
int ct = 5;
while(ct)
{
fputs("hello world \\n",stderr);
ct--;
}
a–追加写入
#include <stdio.h>
int main()
{
FILE* fp = fopen("log.txt","a");//append
if(fp == NULL)
{
perror("fopen");
return 1;
}
int ct = 5;
while(ct)
{
fputs("hello L \\n",fp);
ct--;
}
fclose(fp);
return 0;
}
write-- 覆盖写入
#include <stdio.h>
int main()
{
FILE* fp = fopen("log.txt","w");
if(fp == NULL)
{
perror("fopen");
return 1;
}
int ct = 5;
while(ct)
{
fputs("welcome!\\n",fp);
ct--;
}
fclose(fp);
return 0;
}
系统中的I/O
接口
- O_RDONLY 只读打开
- O_WRONLY只写打开
- O_RDWR读写打开
- O_CREAT若文件不存在，则创建
- O_APPEND追加写
- 打开成功返回值 大于0
- 打开失败返回1
文件描述符
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int main()
{
int fd = open("log.txt",O_WRONLY,0666);
printf("fd: %d\\n",fd);
return 0;
}
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int main()
{
int fd = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",fd);
return 0;
}
找标志位
open
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int main()
{
int f1 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f1);
int f2 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f2);
int f3 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f3);
int f4 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f4);
int f5 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f5);
return 0;
}
write&close
const char* msg = "welcome L\\n";
write(1,msg,strlen(msg));
char buff[32];
read(0,buff,32);
printf("%s\\n",buff);
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
int main()
{
int f1 = open("log.txt",O_WRONLY|O_CREAT,0666);
if(f1 < 0){
printf("open error!\\n");
}
printf("fd: %d\\n",f1);
int ct = 5;
const char* msg = "hello world!\\n";
while(ct)
{
write(f1,msg,strlen(msg));//strlen不需要+1
ct--;
}
close(f1);
return 0;
}
read
#include <string.h>
int main()
{
int f1 = open("log.txt",O_RDONLY);
if(f1 < 0){
printf("open error!\\n");
}
printf("fd: %d\\n",f1);
char c;
while(1)
{
ssize_t s = read(f1,&c,1);
if(s <= 0)
{
break;
}
write(1,&c,1);//fwrite(,,,stdout);
}
close(f1);
return 0;
}
文件标识符分配规则
从最小但是没有被使用的开始分配
关闭显示器(1)
close(1);
int f2 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f2);
int f3 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f3);
int f4 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f4);
int f5 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f5);
return 0;
关0
close(0);
int f2 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f2);
int f3 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f3);
int f4 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f4);
int f5 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f5);
return 0;
close(0);
close(2);
int f2 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f2);
int f3 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f3);
int f4 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f4);
int f5 = open("log.txt",O_WRONLY|O_CREAT,0666);
printf("fd: %d\\n",f5);
return 0;
int fd = open("log.txt",O_WRONLY|O_CREAT,0666);
if(fd < 0){
return 1;
}
write(fd,"hello\\n",6);
write(fd,"hello\\n",6);
write(fd,"hello\\n",6);
write(fd,"hello\\n",6);
write(fd,"hello\\n",6);
close(fd);
close(1);
int fd = open("log.txt",O_WRONLY|O_CREAT,0666);
if(fd < 0){
return 1;
}
write(fd,"hello\\n",6);
write(fd,"hello\\n",6);
write(fd,"hello\\n",6);
write(fd,"hello\\n",6);
write(fd,"hello\\n",6);
close(fd);
重定向
输出重定向
close(1);
int fd = open("log.txt",O_WRONLY|O_CREAT,0666);
if(fd < 0){
return 1;
}
write(1,"hello\\n",6);
write(1,"hello\\n",6);
write(1,"hello\\n",6);
write(1,"hello\\n",6);
write(1,"hello\\n",6);
close(fd);
close(1);
int fd = open("log.txt",O_WRONLY|O_CREAT,0666);
if(fd < 0){
return 1;
}
printf("hello you:%d\\n",123);
printf("hello you:%c\\n",'v');
printf("hello you:%f\\n",3.335);
fflush(stdout);
close(1);
int fd = open("log.txt",O_WRONLY|O_CREAT,0666);
if(fd < 0){
return 1;
}
printf("hello",stdout);
printf("hello",stdout);
printf("hello",stdout);
int fd = open("log.txt",O_WRONLY|O_CREAT,0666);
if(fd < 0){
return 1;
}
printf("hello",stdout);
printf("hello",stdout);
printf("hello",stdout);
重定向本质是修改文件描述符下标对应的struct file 指向的内容*
struct FILE 是一个结构体，里面必定包含一个成员叫fd
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
int main()
{
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