Thread: Help on splitting string in C

Do you really want to split MAC addresses at every colon?

> I am trying but its really taking me time
So post what you tried?

> i only need this for a proof of concept script.
So why not prove it with a language with better string support like Python or Perl?

Originally Posted by Salem

Do you really want to split MAC addresses at every colon?

> I am trying but its really taking me time
So post what you tried?

> i only need this for a proof of concept script.
So why not prove it with a language with better string support like Python or Perl?

Hi ,

nope.. that should stay intact. my aim is actually to take
all the content only without the keys.

"Everything after the ':" (colon) as my content"


What i have tried is as below:

Code:

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

int main() {
    
  char* mystr =
  "Packet length: 64 [Bytes], Arrival time: 2018-02-21 12:43:36.877229\n"
  "Ethernet II Layer, Src: 00:04:96:9a:d1:00, Dst: 4c:72:b9:d1:a5:9c\n"
  "IPv4 Layer, Src: 10.221.0.69, Dst: 10.221.79.19\n"
  "TCP Layer, [ACK], Src port: 54671, Dst port: 5900\n"
  "Payload Layer, Data length: 10 [Bytes] Data: 310000780438\n";

   const char s[] = "\r";
   char *token;
   
   /* get the first token */
   token = strtok(mystr, s);
   
   /* walk through other tokens */
   while( token != NULL ) {
      printf( "%s\n", token );
      token = strtok(NULL, s);
   }
}

But still wondering how do i do second level of split upon getting token.

1. Str1 should be an array, not a pointer. A char pointer initialized with "foo" is likely to point to read only memory. This breaks the strtok.
2. It makes no sense to use the same delimiter in both loops.

I have to admit, I did not expect the data to change merely because I pointed out that \r wasn't in it. Resist the urge to just massage your data until your code works. You will rarely have the choice to just change what input your program gets in the real world. It's best to avoid ever doing that if you want to write good working programs.

>Now i do not understand, am i not making any sense in here ? no ?
Yes, you cannot change a string literal. Put your data in an array.

Originally Posted by whiteflags

I have to admit, I did not expect the data to change merely because I pointed out that \r wasn't in it. Resist the urge to just massage your data until your code works. You will rarely have the choice to just change what input your program gets in the real world. It's best to avoid ever doing that if you want to write good working programs.

>Now i do not understand, am i not making any sense in here ? no ?
Yes, you cannot change a string literal. Put your data in an array.

Awesome !

Manage to make it work ! Your guide was extremely helpful and i seriously appreciate the timely answers. Definitely helped me alot.
Else i hv no idea how much more time i would be wasting.

Code:

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

int main() {
    
  char *s_tr =
  "Packet length: 64 [Bytes], Arrival time: 2018-02-21 12:43:36.877229\r\n"
  "Ethernet II Layer, Src: 00:04:96:9a:d1:00, Dst: 4c:72:b9:d1:a5:9c\r\n"
  "IPv4 Layer, Src: 10.221.0.69, Dst: 10.221.79.19\r\n"
  "TCP Layer, [ACK], Src port: 54671, Dst port: 5900\r\n"
  "Payload Layer, Data length: 10 [Bytes] Data: 310000780438\r\n";

    
    char s[strlen(s_tr)];
    strncpy(s,s_tr, sizeof(s));


    char *str1, *str2, *token, *subtoken;
    char *saveptr1, *saveptr2;
    int j;

    for (j = 1, str1 = s; ;j++, str1 = NULL) {
        token = strtok_r(str1, "\r\n", &saveptr1);
        if (token == NULL)
            break;
        printf("%d: %s\n", j, token);

        for (str2 = token; ; str2 = NULL) {
            subtoken = strtok_r(str2, ",", &saveptr2);
            if (subtoken == NULL)
                break;
            printf("	 --> %s\n", subtoken);
        }
    }
    
    
}

Why i have to leave the actual string as a pointer is because that is what i am getting from a function that i do not have access to change.
Hence, i have to do manual conversion of char* to char[] .

Plus , the data originally looks like that, i didnt change, when i posted it for you, i had some old copies that i accidentally posted. Thats why i changed later on.

Originally Posted by whiteflags

Well, as long as you keep in mind that your example is slightly different from a larger program.

I highly doubt that you will have to copy the string you get from a function parameter into another array. The only time you need to be careful is if you know that the object behind the pointer is a string literal. In all likelihood it's probably an array that decayed into a pointer to the first element.

Code:

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

int main() {
    
  char *s_tr =
  "Packet length: 64 [Bytes], Arrival time: 2018-02-21 12:43:36.877229\r\n"
  "Ethernet II Layer, Src: 00:04:96:9a:d1:00, Dst: 4c:72:b9:d1:a5:9c\r\n"
  "IPv4 Layer, Src: 10.221.0.69, Dst: 10.221.79.19\r\n"
  "TCP Layer, [ACK], Src port: 54671, Dst port: 5900\r\n"
  "Payload Layer, Data length: 10 [Bytes], Data: 310000780438";

    
    char s[strlen(s_tr)];
    strncpy(s,s_tr, sizeof(s));


    char *str1, *str2, *token, *subtoken;
    char *saveptr1, *saveptr2;
    int j;

    for (j = 1, str1 = s; ;j++, str1 = NULL) {
        token = strtok_r(str1, "\r\n", &saveptr1);
        if (token == NULL)
            break;
        printf("%d: %s\n", j, token);

        for (str2 = token; ; str2 = NULL) {
            subtoken = strtok_r(str2, ",", &saveptr2);
            if (subtoken == NULL)
                break;
            printf("	 --> %s\n", subtoken);
            
            char *l = strchr(subtoken, ':');
            printf("             --> %s\n", l);
        }
    }
    
    
}

My final code, eventually manage to break it down to its core, except i have a ":" colon infront everyone, nx mission to figure how to remove that lol.

Thanks again!

Share URL: jdoodle.com/a/nB7

> char s[strlen(s_tr)]
You need to add 1 to allow space for the \0, and use strcpy to make sure you copy it.

If you're just trying to extract the data, you might be able to use sscanf.
Partial example:

Code:

#include <stdio.h>

typedef struct Packet {
    int packet_length;
    struct {int year, month, day;} date;
    struct {int hour, minute, second, microseconds;} time;
    char src[20], dst[20];
} Packet;

int main() {
    char s[] =
        "Packet length: 64 [Bytes], Arrival time: 2018-02-21 12:43:36.877229\n"
        "Ethernet II Layer, Src: 00:04:96:9a:d1:00, Dst: 4c:72:b9:d1:a5:9c\n"
        "IPv4 Layer, Src: 10.221.0.69, Dst: 10.221.79.19\n"
        "TCP Layer, [ACK], Src port: 54671, Dst port: 5900\n"
        "Payload Layer, Data length: 10 [Bytes], Data: 310000780438\n";
    Packet p;
    sscanf(s, "Packet length: %d [Bytes], Arrival time: %d-%d-%d %d:%d:%d.%d\n"
              "Ethernet II Layer, Src: %[^,], Dst: %s\n",
           &p.packet_length, &p.date.year, &p.date.month, &p.date.day,
           &p.time.hour, &p.time.minute, &p.time.second, &p.time.microseconds,
           p.src, p.dst);
    printf("%d\n%d %d %d\n%d %d %d %d\n%s\n%s\n",
       p.packet_length, p.date.year, p.date.month, p.date.day,
       p.time.hour, p.time.minute, p.time.second, p.time.microseconds,
       p.src, p.dst);
    return 0;
}

Note that I added a seemingly-missing comma after "[Bytes]" in the last line.