strchr, memchr fails to locate the character - c++

Question

I am trying to parse a string of format something like 1-3,5-7. I need to read 1,3 and 5,7.
What I am doing
char *dup_string;
dup_string = strdup(data);
tok = strtok(dup_string, ",");
while (tok != NULL)
{
char *rangeTok;
rangeTok = (char *)memchr(tok, "-", strlen(tok));
startpage = atoi(tok);
if(rangeTok != NULL)
{
*rangeTok++;
endpage = atoi(rangeTok);
}
else
endpage = startpage;
tok = strtok(NULL,",");
}
Here memchar returning a badptr, I have tried using strchr which is also returning batptr. Any ideas why it is returning badptr.
FYI, earlier I tried:
tok = strchr(dupstring, ",");
which worked fine for sometime, and started returning badptr. I am not sure why it is doing that.

Answer 1

You're passing the wrong argument to both strchr and memchr, as has already been pointed out. The second argument is an integer holding the value of a character, not a const char *.
This line
rangeTok = (char *)memchr(tok, "-", strlen(tok));
should be either
rangeTok = (char *)memchr(tok, '-', strlen(tok));
or preferably
rangeTok = strchr(tok, '-');
As an aside, what is this badptr? Do you just mean NULL?

Answer 2

The prototype of memchr() is as follows, void * memchr(void * ptr, int value, size_t num);. But you are passing a string in memchr(tok, "-", strlen(tok)); instead of an integer. The way you used strtok() is also wrong, It should be as follows,
tok = strtok(dup_string, ",");
while (tok != NULL)
{
/* Body of Loop */
tok = strtok(NULL,",");
}
On a first call, strtok() expects a string as the first argument, whose first character is used as the starting location to scan for tokens. In subsequent calls, the function expects a null pointer and uses the position right after the end of last token as the new starting location for scanning.

Answer 3

try to use sscanf() in this way
#include<stdio.h>
#include<string.h>
main()
{
char *data = "1-3,5,8-9";
char *ptr = data;
int e, pos=0, startpage, endpage;
while((e=sscanf(ptr, "%d-%d%n", &startpage, &endpage, &pos))>=1)
{
ptr+=pos;
if(e==1)
endpage = startpage;
printf("start page %d ** end page %d\n",startpage,endpage);
if (sscanf(ptr, " %*[,]%n", &pos) >= 0)
ptr+=pos;
}
}