Re: programming using system calls

[Mateus Interciso <p.zarnick@gmail.com>]

On Tue, 31 Jul 2007 18:00:03 +0400,
Андрій Мішковський wrote:

> Hi, Mateus.
> Maybe it looks rude, but i want to correct you: fread, feof, fopen are
> _not_ system calls, as i remember. Your example is correct, but it makes
> no use of system calls. Your code is pure ISO C. :)
> Considering this, the program should look like this:
> 
> #include <unistd.h> /*read(), close()*/ #include <fcntl.h> /*open()*/
> #include <stdio.h> /*fprintf()*/
> #include <sys/types.h> /**/
> #include <errno.h> /* errno*/
> #include <string.h> /* strerror(), memset()*/
> 
> int
> main(int argc, char **argv)
> {
> 	int fd; /*file descriptor*/
> 	char buf[BUFSIZ]; /*buffer for reading data*/ int bytes_read = -1;
> 	/*bytes, already read from file*/
> 	
> 	if (argc != 2)
> 	{
> 		fprintf(stderr, "Usage: %s <file>\n", argv[0]); return 1;
> 	}
> 	
> 	fd = open (argv[1], O_RDONLY);
> 	if (fd == -1)
> 	{
> 		fprintf(stderr, "%s: open() failed. Reason: %s", argv[0],
> 		strerror(errno)); return 1;
> 	}
> 	
> 	while (bytes_read != 0)
> 	{
> 		bytes_read = read(fd, buf, BUFSIZ);
> 		if (bytes_read == -1)
> 		{
> 			fprintf(stderr, "%s: read() failed. Reason: %s", 
argv[0],
> 			strerror(errno)); close(fd);
> 			return 1;
> 		}
> 		fprintf(stdout, "%s", buf);
> 		memset(buf, 0, BUFSIZ);
> 	}
> 	
> 	close(fd);
> 	
> 	return 0;
> }
> 
> 2007/7/31, Mateus Interciso <p.zarnick@gmail.com>:
>> On Tue, 31 Jul 2007 04:27:13 -0700, nisa wrote:
>>
>> > hi,
>> > i am quite new to programming using system calls and would like a
>> > basic idea regarding the usage of system calls. i would like
>> > assistance in the following area of c programming in linux: 1.how to
>> > open a text file ,read data and print the data on console using
>> > system calls
>> > 2.create a text file and write some data 3.read data from a file and
>> > append that data to another file using lseek() 4.creation of a parent
>> > and child process using fork()
>>
>> Well, just to not let you in blank, here is a VERY simple file that
>> reads a text file, and output it to the screen
>>
>> #include <stdio.h>  //standard IO
>> #include <stdlib.h> //for reading files #include <string.h> //for
>> memset
>> #include <errno.h>  //for errno
>> int main(int argc, char *argv[]){
>>   FILE *fp = NULL;
>>   char ch[1];
>>
>>   if(argc!=2){
>>     fprintf(stderr,"Usage:%s <file>\n",argv[0]); return 1;
>>   }
>>   memset(ch,'\0',sizeof(char)*1);
>>   if((fp=fopen(argv[1],"r"))==NULL){
>>     perror("fopen");
>>     return errno;
>>   }
>>   while(feof(fp)==0){
>>     if( (fread(ch,sizeof(char),1,fp)==0) && (feof(fp)==0) ){
>>       perror("fread");
>>       fclose(fp);
>>       memset(ch,'\0',sizeof(char)*1);
>>       return errno;
>>     }
>>     fprintf(stdout,"%c",ch[0]);
>>   }
>>   fclose(fp);
>>   memset(ch,'\0',sizeof(char)*1);
>>   return 0;
>> }
>>
>> Also, as it was stated before, use the man pages. If you don't have a
>> Linux box, then google will be your friend for this. In this example,
>> you would need, the man pages for fopen(),fread() and feof().
>>
>> Good luck.
>>
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>>

You are absolutly right, I'm terrible sorry...It's just that it has been 
so long since I haven't used open(), read(), close(), that I must have 
gone crazy, I'm terribly sorry for this.

Mateus

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