Linux的 C系统调用操作 ,下面我们就来练习下 简单的系统调用操作
read系统调用测试
/*************************************************************************> File Name: read.c> Author: > Mail: > Created Time: Tue 10 Feb 2015 01:23:58 AM PST ************************************************************************/#include<stdio.h>#include<unistd.h>#include<errno.h>//利用管道测试程序的标准输入//echo hello world | ./read// ./read < a.txt int main(){char buf[128] ;int len ;//从输入流读取数据进入到buffer 如果返回-1 那么说明读取错误if((len=read(0,buf,128))==-1){//错误写入标准错误输出write(2,"read error\n",11) ;}//将通过标准输入读取的数据通过标准输出输出到控制台if(write(1,buf,len)!=len){//如果输出的长度不等于 len 说明 IO错误write(2,"read error\n",11) ;}exit(0);return 0 ;}
write系统调用测试
/*************************************************************************> File Name: write.c> Author: > Mail: > Created Time: Tue 10 Feb 2015 12:39:05 AM PST ************************************************************************/#include<stdio.h>//Linux和 Uninx有关与系统调用的封装#include<unistd.h>//errno系统最后一次错误#include<errno.h>//通过自动打开文件句柄 1 也就是标准输出进行字符串输出 int main(){if(write(1,"hello,world\n",2)!=12){write(2,"write error!\n",13) ;} printf("ErrorNo:%d\n",errno); exit(0) ;}
open系统调用测试1
/*************************************************************************> File Name: open.c> Author: > Mail: > Created Time: Tue 10 Feb 2015 02:07:54 AM PST ************************************************************************/#include <stdio.h>#include <unistd.h>#include <fcntl.h>#include <sys/stat.h>#include <stdlib.h> int main(){char*filein="./in.txt" ;char*fileout="./out.txt" ;int fdin,fdout ;char rdChar ;//以只读方式打开输入文件if((fdin=open(filein,O_RDONLY))==-1){write(2,"OpenError!\n",11) ;return 0 ;}//打开文件 文件不存在并且创建文件文件存在 会 清空文件 并且复给 文件所有者读写权限if((fdout=open(fileout,O_CREAT|O_WRONLY|O_TRUNC,S_IRUSR|S_IWUSR))==-1){//errorwrite(2,"OpenError!\n",11);return 0 ;}//通过系统调用进行文件复制while(read(fdin,&rdChar,1)==1){write(fdout,&rdChar,1) ;}exit(0)return 0 ;}
open系统调用测试2
#include<stdio.h>#include<unistd.h>#include<sys/stat.h>#include<fcntl.h>#include<sys/types.h>int main(){int fdin,fdout,len ;char buf[10] ;fdin=open("./in.txt",O_RDONLY);fdout=open("./out.out",O_WRONLY|O_TRUNC|O_CREAT,S_IRUSR|S_IWUSR) ;//效率比较高的写法 尽量少调用系统调用while((len=read(fdin,buf,10))>0){write(fdout,buf,len) ;}return 0 ;lseek系统调用测试/*************************************************************************> File Name: lseek.c> Author: > Mail: > Created Time: Tue 10 Feb 2015 05:02:51 AM PST ************************************************************************/#include<stdio.h>#include<sys/types.h>#include<unistd.h>#include<fcntl.h>#include<sys/stat.h> #define STD_INPUT 0#define STD_OUTPUT 1#define STD_ERROR 2//函数读取用户输出的第二个和倒数第二个字符 输入字符串大于5int main(){char input[256] ;int rdLen,wLen ;int fdwrite,fdread;char rdChar;rdLen=read(STD_INPUT,input,256);if(rdLen==-1){write(STD_ERROR,"error\n",6);exit(0);}if((fdwrite=open("./res.txt",O_CREAT|O_TRUNC|O_WRONLY,S_IRUSR|S_IWUSR))==-1){write(STD_ERROR,"create file error",17);exit(0) ;}wLen=write(fdwrite,input,rdLen);if(wLen==-1)exit(0);close(fdwrite) ;if((fdread=open("./res.txt",O_RDONLY))==-1)exit(0);lseek(fdread,1,SEEK_SET);read(fdread,&rdChar,1) ;printf("Index2:%c\n",rdChar);lseek(fdread,-3,SEEK_END) ;read(fdread,&rdChar,1);printf("Index-2:%c\n",rdChar);close(fdread) ;return 0 ;}
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