read() always returning 0 (not reading)
I am playing around with the read(), write(), and open() system calls. I wrote a function to open/create 3 files, a function to write a test message to the files, and a file to read and print to the terminal what is in the files.
The open and write system calls work fine, if I cat the files they display exactly what they should. When I try to read from the files though my reads are always returning 0, and so not displaying anything from the file.
I tried running the program once, then commenting out the write function. When I do this the read function will read from the files, but the output is unfortunately garbage. I seem to have this sort of trouble when using the read system call and would very much appreciate any help so I can use them properly.
Here are the open and read functions, I have code in the read function to check the values of the fd that the pointers hold and they are correct.
Code:
int openfiles(int *fdp1, int *fdp2, int *fdp3){
/*Open file for appending */
if((*fdp1=open("file1-append", O_RDWR|O_CREAT|O_APPEND,S_IRUSR |S_IWUSR))==-1){
perror("File1 Open Error");
}
/* open file and truncate */
if((*fdp2=open("file2-trunc", O_RDWR|O_CREAT|O_TRUNC, S_IRUSR|S_IWUSR))==-1){
perror("File2 Open Error");
}
/* Open file only if it does not already exist */
if((*fdp3=open("file3-wronce", O_RDWR|O_CREAT|O_EXCL, S_IRUSR|S_IWUSR))==-1){
perror("File3 Open Error");
}
return 0;
}
int readfiles(int *fdp1, int *fdp2, int *fdp3){
printf("\nfdp1:%d,fdp2:%d,fdp3:%d\n",*fdp1,*fdp2,*fdp3);
ssize_t readstatus;
char mybuffer[BUFF_SIZE];
puts("File 1:");
readstatus = read(*fdp1,&mybuffer,BUFF_SIZE);
printf("\nreadstatus:%d\n",readstatus);
while(readstatus > 0){
puts(mybuffer);
printf("\nreadstatus:%d\n",readstatus);
readstatus = read(*fdp1,&mybuffer,BUFF_SIZE);
}
printf("\nreadstatus:%d\n",readstatus);
if(readstatus ==-1){
perror("Error reading File 1:");
exit(1);
}
if((readstatus = read(*fdp2,&mybuffer,BUFF_SIZE))==-1){
perror("Error reading File 2:");
exit(1);
}
printf("\nreadstatus:%d\n",readstatus);
puts("File 2:");
puts(mybuffer);
if((readstatus = read(*fdp3,&mybuffer,BUFF_SIZE))==-1){
perror("Error reading File 3:");
puts("File probably already exists");
}
puts("File 3:");
puts(mybuffer);
return 0;
}
