Weird output from strtok - c

Question

I was having some issues dealing with char*'s from an array of char*'s and used this for reference: Splitting C char array into words
So what I'm trying to do is read in char arrays and split them with a space delimiter so I can do stuff with it. For example if the first token in my char* is "Dog" I would send it to a different function that dealt with dogs. My problem is that I'm getting a strange output.
For example:
INPUT: *cmd = "Dog needs a vet appointment."
OUTPUT: (from print statements) "Doneeds a vet appntment."
I've checked for memory leaks using valgrind and I have none of them or other errors.
void parseCmd(char* cmd){ //passing in an individual char* from a char**
char** p_args = calloc(100, sizeof(char*));
int i = 0;
char* token;
token = strtok(cmd, " ");
while (token != NULL){
p_args[i++] = token;
printf("%s",token); //trying to debug
token = strtok(NULL, cmd);
}
free(p_args);
}
Any advice? I am new to C so please bear with me if I did something stupid. Thank you.

Answer 1

In your case,
token = strtok(NULL, cmd);
is not what you should be doing. You instead need:
token = strtok(NULL, " ");
As per the ISO standard:
char *strtok(char * restrict s1, const char * restrict s2);
A sequence of calls to the strtok function breaks the string pointed to by s1 into a sequence of tokens, each of which is delimited by a character from the string pointed to by s2.
The only difference between the first and subsequent calls (assuming, as per this case, you want the same delimiters) should be using NULL as the input string rather than the actual string. By using the input string as the delimiter list in subsequent calls, you change the behaviour.
You can see exactly what's happening if you try the following code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void parseCmd(char* cmd) {
char* token = strtok(cmd, " ");
while (token != NULL) {
printf("[%s] [%s]\n", cmd, token);
token = strtok(NULL, cmd);
}
}
int main(void) {
char x[] = "Dog needs a vet appointment.";
parseCmd(x);
return 0;
}
which outputs (first column will be search string to use next iteration, second is result of this iteration):
[Dog] [Dog]
[Dog] [needs a vet app]
[Dog] [intment.]
The first step worked fine since you were using space as the delimiter and it modified the string by placing a \0 at the end of Dog.
That means the next attempt (with the wrong spearator) would use one of the letters from {D,o,g} to split. The first matching letter for that set is the o in appointment which is why you see needs a vet app. The third attempt finds none of the candidate letters so you just get back the rest of the string, intment..

Answer 2

token = strtok(NULL, cmd); should be token = strtok(NULL, " ");.
The second argument is for delimiter.
http://man7.org/linux/man-pages/man3/strtok.3.html