符合fgets（）的分段错误-C

Question

I have this code in my program:

char* tok = NULL;
char move[100];

if (fgets(move, 100, stdin) != NULL) 
{
    /* then split into tokens using strtok */
    tok = strtok(move, " "); 

    while (tok != NULL)
    {
        printf("Element: %s\n", tok);
        tok = strtok(NULL, " ");
    }
}

I have tried adding printf statements before and after fgets, and the one before gets printed, but the one after does not. I cannot see why this fgets call is causing a segmentation failure.

If someone has any idea, I would much appreciate it.

Thanks Corey

Answer 1

The strtok runtime function works like this

the first time you call strtok you provide a string that you want to tokenize

char s[] = "this is a string";

in the above string space seems to be a good delimiter between words so lets use that:

char* p = strtok(s, " ");

what happens now is that 's' is searched until the space character is found, the first token is returned ('this') and p points to that token (string)

in order to get next token and to continue with the same string NULL is passed as first argument since strtok maintains a static pointer to your previous passed string:

p = strtok(NULL," ");

p now points to 'is'

and so on until no more spaces can be found, then the last string is returned as the last token 'string'.

more conveniently you could write it like this instead to print out all tokens:

for (char *p = strtok(s," "); p != NULL; p = strtok(NULL, " "))
{
  puts(p);
}

EDITED HERE:

If you want to store the returned values from strtok you need to copy the token to another buffer eg strdup(p); since the original string (pointed to by the static pointer inside strtok) is modified between iterations in order to return the token.