Why is my program not displaying any output?

Question

I am trying to recursively traverse through a directory and list any files that end in .txt or the names of folders.

void listFilesRecursively(char *basePath) {

    char path[1000];
    struct dirent *ptr;
    DIR *dir = opendir(basePath);

    // Unable to open directory
    if (!dir)
        return;

    while ((ptr = readdir(dir)) != NULL) 
    {
        if (strcmp(ptr->d_name,".") != 0 && strcmp(ptr->d_name, "..") != 0)
        {

            char *name = NULL;
            char *type = NULL;

            while (name != "." || name != NULL) {
                name++;
            }

            for (name = ptr->d_name; *name != '\0' ; name++) {

                if (name == '.') {
                    while (*name != '\0') {
                        *type = *name;
                        name++;
                    }
                        break;                      

                } else if (*name == '\0') {
                    printf("%s\n", ptr->d_name);
                }

            }                   

            if (strcmp(type,"txt") == 0)            
                printf("%s\n", ptr->d_name);

            // create new path from our base path
            strcpy(path, basePath);
            strcat(path, "/");
            strcat(path, ptr->d_name);

            listFilesRecursively(path);

        }
    }
        closedir(dir);
}

My expected results would be the files that end in .txt and files that are folders. However, the output is blank and it may go into an infinite loop.

The condition in `while (name != "." || name != NULL)` is always true. (And `name != "."` does not do a string comparison.) — jamesdlin, Mar 28 '19 at 00:27
See [How do I properly compare strings in C?](https://stackoverflow.com/questions/8004237) — Jonathan Leffler, Mar 28 '19 at 00:28
For one thing, you're using the variable `name` as both a character and a pointer. For example, rather than comparing `name` to `"."` and `NULL`, what you really want is to compare `*name` to `'.'` and `'\0'`. — Lee Daniel Crocker, Mar 28 '19 at 00:29
@LeeDanielCrocker: Except `name` is initialized to `NULL`, so it's definitely not okay to compare `*name` to anything at that time. — ShadowRanger, Mar 28 '19 at 00:39

score 0 · Answer 1 · answered Mar 28 '19 at 00:35

This is an infinite loop:

        while (name != "." || name != NULL) {
            name++;
        }

name is a char*. Unless the interned string literal "." is stored at the NULL address (it isn't), then you're saying the loop should continue forever, because name will always be either not pointing to the storage for "." or not pointing to NULL. While I believe it's officially undefined behavior to compare unrelated pointers like "." and name, in practice most (all flat memory model?) compilers just allow arbitrary pointer comparisons, and since you never dereference the pointer, you never actually try to read the unallocated addresses you're traversing (you'd eventually segfault if you did), so it just goes on forever.

I'm unclear on what the goal of that loop is (maybe stripping leading .s from "hidden" file names?), so I can't really suggest a fix other than removing it.

Why is my program not displaying any output?

1 Answers1