CODEWITHSUNDEEP
c
Ionela Alina
Ionela Alina

Reputation: 23

Unique String generator

I want to make a program (network server-client). One of the specification for this program is next:

The server will receive the sent packages and save it into a file, with a unique name (generated by the server at the moment the transfer starts. Ex __tf_"unique_random_string".txt

I made a function that returns a pointer to a "unique" string created.

The problem is: If i stop the server and then start it again it will generate the same names.

Ex:this file names were generated and then i stopped the server.

__ft_apqfwk.txt

__ft_arzowk.txt

__ft_cdyggx.txt

I start it again and i try to generate 3 file names. Them will be the same.

Sorry for my english. I'm still learning it.

My function to generate this "unique string" is:

char *create_random_name(void)
{
    const char charset[] = "abcdefghijklmnopqrstuvwxyz";
    char *file_name;
    int i=0;
    int key;
    if((file_name = malloc(16 * sizeof ( char )) ) == NULL)
    {
        printf("Failed to alloc memory space\n");
        return NULL;
    }
    strcpy(file_name,"__ft_");
    for(i=5 ; i<11 ; i++)
    {
        key = rand() % (int)(sizeof(charset)-1);
        file_name[i]=charset[key];
    }
    strcat(file_name,".txt");
    file_name[15] = '\0';
    return file_name;
}

Upvotes: 2

Views: 1303

Answers (4)

user3629249
user3629249

Reputation: 16540

Before calling rand(),--- once and only once---, call srand(time()) to initialize the random number generator.

Before settling on any specific file name, call stat() to assure that file name does not already exist.

Upvotes: 0

ShadowRanger
ShadowRanger

Reputation: 155438

If it's available, you could avoid manually generating random names that might collide and let the system do it for you (and handle collision resolution by creating a new name) by using mkstemps. This is also safer because it opens the file for you, removing the risk of a random name being generated, verified to be unique, then trying to open it and discovering another thread/process raced in and created it.

char name[] = "/path/to/put/files/in/__ft_XXXXXX.txt";
int fd = mkstemps(name, strlen(".txt"));
if (fd == -1) { ... handle error ... }

After mkstemps succeeds, name will hold the path to the file (it's mutated in place, replacing the XXXXXX string), and fd will be an open file descriptor to that newly created file; if you need a FILE*, use fdopen to convert to a stdio type.

Upvotes: 0

MRBULL93
MRBULL93

Reputation: 161

Your question seems a little bit unclear but if you want to generate a unique string there are a couple of things you can consider:

  1. Get System timestamp ( yyyy-MM-dd-HH-mm-ss-fff-tt)
  2. Use Random function to generate a random number

Combine this with your function and I am sure you will get a unique string.

Hope it helps !

Upvotes: 1

user5940189
user5940189

Reputation:

One option is saving to a file the names that have been used, and using them as a checklist. You also want to seed rand with something like srand(time(NULL)).

another is ignoring the randomisation, and just going in order, e.g. aaa, aab aac...aba ,abb etc. Again, save where your cycle is up to on a file.

Upvotes: 2

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