Results Of A Variable Into An Array Using C Language Post: 302929345

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Top Forums Programming Results Of A Variable Into An Array Using C Language Post 302929345 by Corona688 on Friday 19th of December 2014 04:36:37 PM

12-19-2014

Registered User

C does not change what variables do depending on their type, or do anything for you when you ask it to convert one type to another. At best, it will ball it up and cram it through the mail slot, i.e. take you completely literally rather than doing the extra work you wanted.

So, if you want the string to be split, you're going to have to tell it to split it.

strtok is fairly good at doing that. It breaks strings apart on a list of letters, any letter in the list is considered a separator. (I add \n to remove newlines from the end while its at it.)

Two caveats:

It modifies buf. For example, the line a:b:c:d:e\n would become a\0b\0c\0d\0e\0. So you can't call it on anything you can't modify, i.e. strtok("a:b:c:d:e", ":"); would crash.
It returns pointers to things inside buf. Every time you overwrite buf[], i.e. every time you call fgets(), all the pointers strtok() gave you last time will point anywhere or nowhere.

Code:

int main()
{
        char buf[512];
        FILE *fp=fopen("/etc/passwd", "r");

        while(fgets(fp, 512, stdin) != NULL)
        {
                char *tok[64], ntok=1;

                tok[0]=strtok(buf, ":\n");
                // strtok() will keep returning more strings until
                // it runs out and returns NULL.
                tok[ntok]=strtok(NULL, ":\n"); 

                while(tok[ntok] != NULL) tok[++ntok]=strtok(NULL, ":\n");

                if(strcmp(tok[0], "bigbadwolf") == 0) puts(tok[0]);
        }
        fclose(fp);
}

Last edited by Corona688; 12-19-2014 at 05:48 PM..

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strtok_r

STRTOK(3)						     Linux Programmer's Manual							 STRTOK(3)

NAME

       strtok, strtok_r - extract tokens from strings

SYNOPSIS

       #include <string.h>

       char *strtok(char *s, const char *delim);

       char *strtok_r(char *s, const char *delim, char **ptrptr);

DESCRIPTION

       A `token' is a nonempty string of characters not occurring in the string delim, followed by  or by a character occurring in delim.

       The strtok() function can be used to parse the string s into tokens. The first call to strtok() should have s as its first argument. Subse-
       quent calls should have the first argument set to NULL. Each call returns a pointer to the next token, or NULL  when  no  more  tokens  are
       found.

       If  a  token ends with a delimiter, this delimiting character is overwritten with a  and a pointer to the next character is saved for the
       next call to strtok().  The delimiter string delim may be different for each call.

       The strtok_r() function is a reentrant version of the strtok() function, which instead of using its own static buffer, requires	a  pointer
       to a user allocated char*. This pointer, the ptrptr parameter, must be the same while parsing the same string.

BUGS

       Never use these functions. If you do, note that:

	      These functions modify their first argument.

	      These functions cannot be used on constant strings.

	      The identity of the delimiting character is lost.

	      The strtok() function uses a static buffer while parsing, so it's not thread safe. Use strtok_r() if this matters to you.

RETURN VALUE

       The strtok() function returns a pointer to the next token, or NULL if there are no more tokens.

CONFORMING TO

       strtok()
	      SVID 3, POSIX, BSD 4.3, ISO 9899

       strtok_r()
	      POSIX.1c

SEE ALSO

       index(3), memchr(3), rindex(3), strchr(3), strpbrk(3), strsep(3), strspn(3), strstr(3)

GNU
								    2000-02-13								 STRTOK(3)

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