Dividing up a char array to different values in struct

Question

Through a tcp socket I get a string like this: "SmallTitle fromhost 9595".

Upon reciving it I would like to divide it in to a struct so it's easier to work with.

This is what I have come up with. But there are problems. 1 it is nasty. 2 When printing the struct in the end i recieve garbage output after the string. See output example at the bottom. Should not printf stop at '\0'? Then it might be missing such.

struct recieved {
    char what[50];
    char from[50];
    int value;
};


int main(int argc, char const *argv[]) {
    struct recieved leaderRec;

    char *word;
    char buf[] = "leadervalue host 9569"; //Example recieved input from socket.

    word = (char *) malloc(sizeof(char) * 50);
    int i = 0;
    int count = 1;

    do{
        if((buf[i] == ' ') || (buf[i+1] == '\0')){
            //End of word
            //word[strlend(word)+1] = '\0';
            //printf("%s\n", word);
            if(count == 3){
                //The value is here
                //get the last number
                strncat(word,&buf[i], 1);
                leaderRec.value = atoi(word);
                //printf("%d\n", value);
            }

            if(count == 1)
                strncpy(leaderRec.what, word, strlen(word));
            else if(count == 2)
                strncpy(leaderRec.from, word, strlen(word));
            free(word);
            word = (char *) malloc(sizeof(char) * 50);
            count++;
        }
        else {
            //printf("%d\n",i );
            //printf("%s\n", &buf[i]);
            strncat(word,&buf[i], 1);
        }
        //printf("%s", &buf[i]);
        //printf("%d -", i);
        i++;
    } while(buf[i] != '\0');

    printf("%s\n", leaderRec.what);
    printf("%s\n", leaderRec.from);
    printf("%d\n", leaderRec.value);
    return 0;
}

Output:

leadervalue
host__vdso_get
9569

Any better ways to do this? How would I avoid the garbage output at the second print in the example output?

Note that the way you are using malloc() makes it look like you don't understand what malloc() is for. Likely your strncpy() migh be a little bit wrong. I just never use it, because IMHO it's better to use memcpy() and write the '\0' by hand. — Iharob Al Asimi
– Iharob Al Asimi, Commented Feb 20, 2018 at 19:19
This is mystery to me — word = (char *) malloc(sizeof(char) * 50); /*...*/ free(word); word = (char *) malloc(sizeof(char) * 50); — Weather Vane
– Weather Vane, Commented Feb 20, 2018 at 19:24
... which you could acheive with word = malloc(50); *word = '\0'; — Weather Vane
– Weather Vane, Commented Feb 20, 2018 at 19:50

MFisherKDX · Accepted Answer · 2018-02-20 20:10:35Z

2

But there are problems. 1 it is nasty. 2 When printing the struct in the end i recieve garbage output after the string.

The "garbage" prints, as have been noted in the comments, are because you are not properly null terminating your strings. For instance, you are not initializing word to an empty string (single null character) before calling strncat.

Any better ways to do this?

Most certainly. I'd suggest using strtok as so:

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

struct received {
    char what[50];
    char from[50];
    int value;
};

int main(void)
{
  char buf[] = "leadervalue host 9569";
  struct received leaderRec; 
  /* Initialize leaderRec here */      
  memset(&leaderRec, 0, sizeof(leaderRec));

  char *s = strdup(buf);
  char *p = strtok(s, " ");
  if (p != NULL) {
     strncpy(leaderRec.what, p, sizeof(leaderRec.what));
     p = strtok(NULL, " ");
  }
  if (p != NULL) {
     strncpy(leaderRec.from, p, sizeof(leaderRec.from));
     p = strtok(NULL, " ");
  }
  if (p != NULL) {
     leaderRec.value = atoi(p);
  }
  free(s);

  printf("%s %s %d\n", leaderRec.what, leaderRec.from, leaderRec.value);
  return 0;
}

edited Feb 20, 2018 at 20:10

answered Feb 20, 2018 at 19:49

MFisherKDX

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1 Comment

Weather Vane Over a year ago

That's true, I'll delete my first comment: I gave UV before commenting anyway.

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