hi
i want to read the contents of a file and show it on screen
i have this code but it doesn't work.can you help me.

char buffertest[1000]="";
char msg[1000]="";
int out;
if(out=open(path4,O_RDONLY)==-1)
{
perror("Error opening file");
}

else {
while(numread=read(out,buffertest,1)>0)
{
strcat(msg,buffertest);
}
puts(msg);

}


The file in path4 will be opened but nothing will be read

Just looking at the code i would think nothing is printed out since the printing is inside the else of the if statement. do something like thischar

buffertest[1000]="";
char msg[1000]="";
int out;
bool fileOpen = true;
if(out=open(path4,O_RDONLY)==-1)
{
perror("Error opening file");
fileOpen = false;
}

if(fileOpen)
{
while(numread=read(out,buffertest,1)>0)
{
strcat(msg,buffertest);
}
puts(msg);
}

That should allow the while loop to run if the file is opened.

I went ahead and copied your code, and tried it myself. The results were quite surprising; i got the same results as you, though i could see nothing wrong with the code. I noticed that the file handle 'out' was being set to zero, which was causing input to be taken from stdin! So i tried changing the open statement:

which i changed to two lines:

this gave me a valid file handle, and the logic worked fine!

Maybe a gcc bug?

Let me know if this fixes things on your system.

here is the bug in assinging and checking

try with,
value returned by the open function after assigning to out variable and then only should be checked for error (-1)

you neednot change the above lines to two (there is nothing wrong in that actually)

this would suffice !!!

actually the problem is not with opening the file but with reading from file.The file will be opend and the value of out will be 0 it goes into else part but it doeant show the contents of the file.Is my read command right or not?

Not quite true, since what is returned from the open function is the file descriptor. This is then passed into the read function. However if (as others have pointed out) this is not being set up correctly then the read will fail because it is trying to read from an invalid file descriptor.

I suggest that you change the code of the open as suggested and you should then have a valid fd and will then be able to read the file.

graeme.

Breaking the if statement into two lines, or enclosing the file handle assignment within quotes in one line ends up achieving the same end. The problem with the original if clause was not a gcc bug as i first thought, but it's just how most C compilers evaluate any expression: from right to left. So the right-most part of the original if clause evaluates to false or zero, since any valid file handle returned by open() will be a positive integer. The result of this evaluation, which is zero, is then assigned to the variable 'out' in the left part. You don't want the file handle to be zero; that's the file handle for stdin (the keyboard)!

Enclosing the left-hand part in parenthesis forces that part to be evaluated first, which assigns a valid file handle to 'out'. Breaking into two lines does the same thing

what programming language is this ?

It looks like C to me but I guess it could be something else...

what i was thinking but lack of a stream anywhere confused me. I see now there using the open command rather then the fopen command.
open is a low level c command for file manipulation it returns a file descriptor. as far as me im not famillar with using it really i always use fopen command cause its eazier to work with.

fopen is std I/O routine which internally makes use of open system call when std I/O buffers get filled.

Rather a write system call associated with open call flushes the buffer each time a write is made.

Hence for frequent writes with less no of characters - fopen and fwrite would suit to.
For less no of writes and bulk characters open and write would fit in.

But still usage depends upon the write frequency, application criticality, integrity needed.