c++ - Why does this use of strtok() cause segmentation fault? -

i trying tokens in string using strtok() , convert them integers. after getting 1 token, trying pull promptly segfaults - how tell system not segfault condition can complete?

code:

char * token; while ( getline (file,line) ) {   char * charstarline = const_cast<char*>(line.c_str()); //cast charstar   char * token;   token = strtok(charstarline," ");         token = strtok(charstarline," ");   int inttoken = atoi(token);   cout << "int token: " << inttoken << endl;   while (token != null)   { token = strtok (null, " "); int inttoken = atoi(token); cout << "int token (loop): " << inttoken << endl;   } 

is casting away const why segfaults? if how around this?

const discussion aside, real problem;

while (token != null)                // last token, not null {   token = strtok (null, " ");        // no more tokens makes go null here   int inttoken = atoi(token);        // , use null right away *boom*                                      // before checking pointer.   cout << "int token (loop): " << inttoken << endl; }