Character array prints garbage unless I increase array size

Question

I am working on a project and I have to increase the size of an array or it prints garbage.

This variable is declared in main

char *fullPath[150];

Then I ask a user a question using this

printf("Enter full path where you want the file to be.\nExample: C:\\Windows\\System32\n");
scanf("%s", &fullPath);

Then I check that this directory exists using

CheckDirectory(fullPath);

Which is my function that looks like...

void CheckDirectory(char *d) {
    DIR* dir = opendir(d);
    char answer[2];

    if (dir) {
        printf("Directory Exists!\n");
        closedir(dir);
    } else if (ENOENT == errno) {
        printf("Directory does not exist.\n");
        printf("Do you want to create this directory? y/n:");
        scanf("%s", &answer);
        if (strcmp(answer, "y") == 0) {
            printf("Ok creating directory\n");
            MakeDirectory(d);
        } else {
            printf("ok not gonna make it");
            exit(1);
        }
    } else {
        printf("Some magical error.");
    }
}

So the above code just basically asks a user for a directory and then puts it into fullPath[150] and then runs tests on it. The next part of the script which is where I run into errors is..

CopyNewFile(fullPath, fileName, argv[0]);

An the function looks like..

void CopyNewFile(char *dir, char *fname, char *curName) {
    char fullDir[350];
    char file[60];

    strncat(file, curName, 20);
    strncat(file, ".exe", 5);
    strncat(fullDir, dir, 250);
    strncat(fullDir, "\\", 5);
    strncat(fullDir, fname, 30);
    if (CopyFile(file, fullDir, FALSE)) {
        printf("\n\nCopied new file.\n\n");
    } else {
        printf("Did not copy.");
    };
}

Now, here is the issue. When I try to run this, it won't copy unless

char fullDir[350];

Is more than 300. I tried 350 and it works, but I haven't tested to find the exact number where it does and does not work. If I it 300, then the fullDir and file gets garbage characters in front of it.

I assume it is something to do with the way memory is allocated but instead of increasing the size of the character arrays I would like to fix it.

Answer 1

char *fullPath[150];

declares 150 pointers of char *. You need

char fullPath[150];

then

scanf("%149s", fullPath);

or you're passing the wrong pointer type to scanf.

(note the lack of & and the size limiter to avoid buffer overflow when entering the path)

The next error (as seen in comments), which (now I realize) is probably the one which triggers the symptoms you're getting:

char file[60];
strncat(file, curName, 20);

that is plain wrong (same for fullDir) because file isn't initialized. One quickfix would be:

char file[60];

But as mentionned with Lundin in comments, it's better to avoid strncat altogether) You could replace the whole strncat block by:

sprintf(file,"%55s.exe",curName);
sprintf(fullDir, "\\%347s", fname);

(trying to compute the max amounts of chars to avoid overflow there also)

or a more classical approach using first strcpy then strcat (no length checking though)

Answer 2

You never initialized the variable file before you concatenate to it. Change it like this. Same with fullDir.

char file[60] = {0};

strncat(file, curName, 20);