Split C string into tokens using sscanf

Question

I'm trying to split a string into tokens but somewhat recursively. I am trying to parse:

"content=0&website=Google"

so that I have a way to take out the parameters and values. If I try strtok I end up destroying the string I want to parse twice. So I tried

char *contents = "content=0&website=Google"
char arg[100];
char value[100];
sscanf(contents, "%s&%s", arg, value);

as a first pass, hoping to parse arg again, but it fails, and arg contains the entire string. I tried using "%s\&%s" thinking & was a reserved word, but no luck there.

Help!

Edit:

This was my strtok hack:

static void readParams(char * string, char * param, char * value) {
    printf("This is the string %s\n",string);
    char * splitted = strtok (string,"=");

    while (splitted != NULL)
    {
        printf("This is the string %s\n",splitted);
        splitted = strtok (NULL, "=");
        // Then do some saving to param and value
    }
}
char * splitted = strtok (contents,"&");
int counter = 0;

while (splitted != NULL)
{
    char * t_str = strdup(splitted);
    readParams(t_str, param, value);
    splitted = strtok (NULL, "&");
}

but it doesn't work because splitted's strtok at the end becomes gobbldygook.

@S.O users I my perception this is a very nice question. In addition to predicting other methods it will be better if someone reason for why the sscanf(contents, "%s&%s", arg, value); doesn't work — Muthu Ganapathy Nathan, Mar 06 '12 at 06:26
@EAGER_STUDENT like I said in my answer, asking `scanf` to scan for `%s` causes it to scan up to the next whitespace. So it won't stop on an ampersand. — Tommy, Mar 06 '12 at 06:56

score 9 · Answer 1 · answered Mar 06 '12 at 06:11

9

Here is a solution that seems to work:

char *contents = "content=0&website=Google";
char arg[100] = {0};
char value[100] = {0};
sscanf(contents, "%[^&]&%s", arg, value);
printf("%s\n%s\n", arg, value);

answered Mar 06 '12 at 06:11

Donotalo

12,748
25
83
121

score 1 · Answer 2 · answered Mar 06 '12 at 06:01

1

scanf is more primitive than you seem to think — %s will match everything up to the next whitespace. Your best solution is probably to stick with strtok but throw it only content you've strduped from the authoritative original.

answered Mar 06 '12 at 06:01

Tommy

99,986
12
185
204

When I try to abstract the sub-parsing into a new function passing in a strduped version of the split, it fails. Why is this? I've added code to the above to fix. – Rio Mar 06 '12 at 06:28

score 0 · Answer 3 · answered Mar 06 '12 at 06:04

0

I recommend something similar to the following:

char t_str[100];
strncpy(t_str, contents, 100);
//now strtok() on t_str, original contents will be preserved

answered Mar 06 '12 at 06:04

RootsAmongRuins

101
1
7

Split C string into tokens using sscanf

3 Answers3

Linked