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Full Discussion: help with opening files and reading them in C
Top Forums Programming help with opening files and reading them in C Post 302495425 by jim mcnamara on Thursday 10th of February 2011 07:56:42 AM
Old 02-10-2011
Code:
#include <unistd.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
// questions 1 & 2:
// access validates access to a file  F_OK == path is okay and file exists  
//  R_OK == F_OK + I can read it, so use R_OK
// Q3:
// this is a general function to get the size of an opened file
size_t filesize(int fd)
{
    struct stat st;
    if(fstat(fd, &st)== -1)
    {
          perror("Cannot stat file");
          exit(1);
    }
    return st.st_size;
}
int main(int argc, char **argv)
{
    FILE *in=NULL; 
    
    if(access(argv[1], R_OK)==0)
    {
           printf("file %s, access is okay\n", argv[1]);
    }
    in=fopen(argv[1],"r");
    printf("file size = %u\n", filesize(fileno(in));
    fclose(in);
    return 0;
}

 

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LEARN ABOUT REDHAT

tcl_access

Tcl_Access(3)						      Tcl Library Procedures						     Tcl_Access(3)

__________________________________________________________________________________________________________________________________________________

NAME

       Tcl_Access, Tcl_Stat - check file permissions and other attributes

SYNOPSIS

       #include <tcl.h>

       int
       Tcl_Access(path, mode)

       int
       Tcl_Stat(path, statPtr)

ARGUMENTS

       char *path (in)			  Native name of the file to check the attributes of.

       int mode (in)			  Mask	consisting  of	one  or  more  of R_OK, W_OK, X_OK and F_OK.  R_OK, W_OK and X_OK request checking
					  whether the file exists and  has  read,  write  and	execute   permissions,	respectively.	F_OK  just
					  requests checking for the existence of the file.

       struct stat *statPtr (out)	  The structure that contains the result.
_________________________________________________________________

DESCRIPTION

       As  of  Tcl 8.4, the object-based APIs Tcl_FSAccess and Tcl_FSStat should be used in preference to Tcl_Access and Tcl_Stat, wherever possi-
       ble.

       There are two reasons for calling Tcl_Access and Tcl_Stat rather than calling system level functions access and stat directly.  First,  the
       Windows	implementation	of  both  functions  fixes  some bugs in the system level calls.  Second, both Tcl_Access and Tcl_Stat (as well as
       Tcl_OpenFileChannelProc) hook into a linked list of functions.  This allows the possibility to reroute file access to alternative media	or
       access methods.

       Tcl_Access checks whether the process would be allowed to read, write or test for existence of the file (or other file system object) whose
       name is pathname.   If pathname is a symbolic link on Unix, then permissions of the file referred by this symbolic link are tested.

       On success (all requested permissions granted), zero is returned.  On error (at least one bit in  mode  asked  for  a  permission  that	is
       denied, or some other  error occurred), -1 is returned.

       Tcl_Stat  fills the stat structure statPtr with information about the specified file.  You do not need any access rights to the file to get
       this information but you need search rights to all directories named in the path leading to the file.  The  stat  structure  includes  info
       regarding device, inode (always 0 on Windows), privilege mode, nlink (always 1 on Windows), user id (always 0 on Windows), group id (always
       0 on Windows), rdev (same as device on Windows), size, last access time, last modification time, and creation time.

       If path exists, Tcl_Stat returns 0 and the stat structure is filled with data.  Otherwise, -1 is returned, and no stat info is given.

KEYWORDS

       stat, access

Tcl									8.1							     Tcl_Access(3)
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