CODEWITHSUNDEEP
cstring
boltup_im_coding
boltup_im_coding

Reputation: 6665

How to use strtok to parse string at whitespace?

I am trying to use strtok() to parse a string deliminated by spaces. From what I can tell, I am using it correctly, but it won't run on ideone.com. Is there anything wrong with the following code? I just get Runtime error time: 0 memory: 2288 signal:11

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

static void test(char *command)
{
    char* output = strtok(command, " ");
    printf("%s\n", output);
}

int main(void) {

    test("set_rate 200");

    return 0;
}

Here it is on ideone.com if you want to try it.

Upvotes: 4

Views: 1695

Answers (4)

Gangadhar
Gangadhar

Reputation: 10516

When you pass hard coded string that was stored in read-only memory.

strtok() does not work with string which is read-only memory.

You need to use string variable rather than string literal .

you can first store string in some variable and then you can pass it to the function.

char[]="set_rate 200";
test(str);

See example: 

 char *str = malloc(20);
    char *tok = NULL;
    int len = 0;

    strcpy(str, "This is a string");
    len = strlen(str);

    printf("string before strtok(): %s\n", str);
    tok = strtok(str, " ");
    while (tok) {
        printf("Token: %s\n", tok);
        tok = strtok(NULL, " ");
    }

Edit

From @Yu Hao comment i am adding this 

char *str = "set_rate 200"; 
test(str); // This won't work. here str is pointer to the string literal.

Upvotes: 2

Jonathon Reinhart
Jonathon Reinhart

Reputation: 137467

Always consult the man pages first.

strtok(3) says:

Be cautious when using these functions. If you do use them, note that:

  • These functions modify their first argument.

  • These functions cannot be used on constant strings.

Upvotes: 4

Yu Hao
Yu Hao

Reputation: 122433

strtok will modify the string passed as the first parameter, so you can't pass a string literal, change your main like this:

int main(void) {  
    char str[] = "set_rate 200";
    test(str);
    return 0;
}

str here is an char array, but not a string literal.

Upvotes: 3

goji
goji

Reputation: 7112

As strtok modifies the string, it requires that the string is not in read-only memory. So when you pass a string literal to your test function, it crashes.

This is better:

char s[] = "set_rate 200";
test(s);

Upvotes: 3

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