strtotok_r and Seg Fault when trying to free()

[pdah]

Hi everybody, I'm having a problem with function strtok_r, it seems that free() function always throws Seg Fault after I use strtok_r.



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

int main()
{
char* hostport = (char *)malloc(100);
char* buf = (char *)malloc(100);

memcpy(hostport,"192.168.0.10:9000/12345678",26);
strtok_r(hostport, ":", &buf);
printf("buf=%s\n",buf);
free(hostport);
free(buf);
return 0;
}


The error message thrown by this script when executing on Ubuntu :


*** glibc detected *** ./a.out: munmap_chunk(): invalid pointer

If I compile this script and run it on Centos, the error message is


*** glibc detected *** ./a.out: free(): invalid pointer


If I comment out the line "free(buf)", there's no error anymore. Can you help me to figure out this problem ?
Thanks in advance.

[monraaf]

char *buf;

Should be enough, no memory allocation and freeing. strtok_r. will use the pointer to point somewhere in the string you passed as the first argument, that's why you are passing a pointer to a pointer and not a pointer ;)

[Can+~]

strtok actually changes the value of the pointer, so after calling it, the content of buf* changes, thus freeing it will try to free a random memory block.

Always read what a function does with your pointers.
http://www.mkssoftware.com/docs/man3/strtok_r.3.asp

[pdah]

Thank you monraaf and Can+~, your posts're really helpful.