Permission Denied When Trying to Append to File C - c

Question

I am attempting to open files and append to them using C. I am dynamically naming the directory based on process Id and creating the filenames based on the "room" that has been randomly selected in the loop. My intention is to open the file, append the room name into the file, and then close the file and move to the next room and perform the same function. The issue I am having is with "open". It seems to only be returning -1, which indicates an error. The error message is stating "Permission denied". I am confused by this because I appear to be setting the proper permissions in the open function. I tried using fopen(), but that kept producing a segmentation fault 11. Is there an issue with my roomFilePath declaration and usage or is my usage of open incorrect? Here is the portion of the code that contains the issue. The makeRooms() function is where I check to see if the file was opened correctly. Thanks!
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <sys/stat.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#define NUM_ROOMS 10
#define NUM_USED_ROOMS 7
#define MAX_CONNECTIONS 6
time_t t;
char* usedRooms[NUM_USED_ROOMS];
int i;
char directoryName[100];
char* baseDirectory = "walterer.rooms.";
int processId;
char roomFilePath[75];
int adjacencyMatrix[7][7] = {0};
int useableConnections;
int e;
int totConnections = 0;
int openRoom;
int file_descriptor;
char* roomNames[] = {
"cleveland",
"columbus",
"dallas",
"toledo",
"miami",
"sarasota",
"boston",
"chicago",
"denver",
"phoenix"
};
int connections[10] = {
0,
0,
0,
0,
0,
0,
0,
0,
0,
0
};
void makeDirectory() {
processId = getpid();
sprintf(directoryName, "%s%d", baseDirectory,processId);
//printf("%s\n", directoryName);
mkdir(directoryName, 777);
}
void makeRooms() {
/* Initializes random number generator */
srand((unsigned) time(&t));
/* Create 7 rooms */
for(i = 0; i < NUM_USED_ROOMS; ){
/* Generate random number between 0 to 10 */
int randomNumber = rand() % NUM_ROOMS;
/* Loop as long the array does not contain any connections at the index */
while(connections[randomNumber] == 0) {
/* Append the room path to the end of my ONID path */
sprintf(roomFilePath,"%s/%s", directoryName, roomNames[randomNumber]);
printf("%s\n",roomFilePath);
/* Create file */
FILE *filePointer;
/* Open file to append*/
//filePointer = open(roomFilePath, O_WRONLY | O_CREAT, 0600);
//!!!Returning -1
file_descriptor = open(roomFilePath, O_APPEND, 0600);
printf("%d\n",file_descriptor);
if (file_descriptor == -1)
{
printf("open() failed on \"%s\"\n", roomFilePath);
perror("In createRooms()");
exit(1);
}
/*if (filePointer == NULL)
{
fprintf(stderr, "Error Creating File\n");
printf("something went wrong with read()! %s\n", strerror(errno));
}*/
/* Print the room name in the file */
/* SEG FAULT HERE!!!! */
fprintf(filePointer, "ROOM NAME: %s\n", roomNames[randomNumber]);
/* Close the file */
//fclose(filePointer);
usedRooms[i] = roomNames[randomNumber];
connections[randomNumber] = 1;
//printf("Room %d is %s \n", i+1, roomNames[randomNumber]);
i++;
}
}
}

Answer 1

First, you're missing part of the required flags argument to open() in this line:
file_descriptor = open(roomFilePath, O_APPEND, 0600);
The only open() flag you're passing is O_APPEND, but open() also requires at least one of the O_RDONLY, O_WRONLY, O_RDWR, O_EXEC, or O_SEARCH flags. (the last two are rarely used.)
Your code should be something like
file_descriptor = open(roomFilePath, O_RDONLY | O_APPEND, 0600);
Per the POSIX standard for open():
SYNOPSIS
#include <sys/stat.h> #include <fcntl.h>
int open(const char *path, int oflag, ...);
...
Values for oflag are constructed by a bitwise-inclusive OR of flags
from the following list, defined in <fcntl.h>. Applications shall
specify exactly one of the first five values (file access modes) below
in the value of oflag:
O_EXEC
Open for execute only (non-directory files). The result is
unspecified if this flag is applied to a directory.
O_RDONLY
Open for reading only.
O_RDWR
Open for reading and writing. The result is undefined if this flag
is applied to a FIFO.
O_SEARCH
Open directory for search only. The result is unspecified if this
flag is applied to a non-directory file.
O_WRONLY
Open for writing only.
In your posted code, of course you get a segmentation fault at this line:
/* SEG FAULT HERE!!!! */
fprintf(filePointer, "ROOM NAME: %s\n", roomNames[randomNumber]);
The filePointer variable has not been initialized in your posted code, so using the value causes a segmentation fault.