Linux C Programming-----file operation (1) Simple operation via system call standard input, standard output, standard error

the C system invoke operation of Linux, Now let's practice the simple system invoke operation .

Read system call Test

/*************************************************************************> File name:read.c> Author: > Mail: > Created time:tue 01:23:58 AM PST **************************************************************** /#include <stdio.h> #include <unistd.h> #include <errno.h>//using standard input//echo hello for piping test procedures  World |./read//./read < a.txt int main () {    char buf[128];    int Len;    Reads data from the input stream into buffer if return-1 then indicates a read error if    ((Len=read (0,buf,128)) ==-1)    {         //error write standard error output         write (2, "read Error\n ", one);    }    Outputs data read through standard input to console if     (write (1,buf,len)!=len)    {           //If the length of the output is not equal to Len description IO error         write (2, "read Error\n ", one);    }    Exit (0);    return 0;}

Write system call Test

/*************************************************************************> File name:write.c> Author: > Mail: > Created time:tue 12:39:05 AM PST **************************************************************** /#include <stdio.h>//linux and Uninx the last error with the encapsulation #include<unistd.h>//errno system called System #include< errno.h>//string output by automatically opening a file handle 1  that is standard output int main () {     if (write (1, "hello,world\n", 2)!=12)    {        Write (2 , "Write error!\n", ();    }   printf ("errorno:%d\n", errno);   Exit (0);}

Open System call Test 1

/*************************************************************************> File name:open.c> Author: > Mail: > Created time:tue 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;        Open the input file as read-only if ((Fdin=open (filein,o_rdonly)) ==-1) {Write (2, "openerror!\n", 11);    return 0; }//Open file file does not exist and create file file exists will empty file and re-write permission to file owner if ((Fdout=open (fileout,o_creat| o_wronly| o_trunc,s_irusr|        S_IWUSR)) (==-1) {//error write (2, "openerror!\n", 11);    return 0;    }//File copy via system call while (read (fdin,&rdchar,1) ==1) {write (fdout,&rdchar,1); }exit (0) return 0;}

Open System call Test 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);     The high efficiency of the writing  system calls as few calls    while ((Len=read (fdin,buf,10)) >0)    {        write (Fdout,buf,len);    }    return 0;

lseek system call Test

/*************************************************************************> File name:lseek.c> Author: > Mail: > Created time:tue 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//function reads the second and second-to-last characters of the user output the input string is greater than 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;}

Linux C Programming-----file operation (1) Simple operation via system call standard input, standard output, standard error