c++ - Error with strtok Function -

in code unhandled expression error when use parse function.

in popstack function right way delete last element of vector.

error is:

unhandled exception @ 0x0f463b50 (msvcr100d.dll) in boost_test.exe: 0xc0000005: access violation writing location 0x00345d49.

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class stack { public:     stack() {globalindex=0; };     std::vector<char*> v;     int globalindex;     void addstack(char* txt);     void parse();     void popstack();     void printstack();  };  void stack::parse() {     char* tok;     tok = strtok(v[globalindex-1], ";");      while(tok!=null)      {         cout<<"\nthe time value = "<<tok<<endl;         tok = strtok(null, " ");      } }     void stack::addstack(char* txt) {  v.push_back(txt); globalindex++;  }    void stack::popstack()   {    v.pop_back();    globalindex--;   }   void stack::printstack()  {  std::cout<<v[globalindex-1]<<endl;  }   int _tmain(int argc, _tchar* argv[]) {  int i;  stack s;  s.addstack("aaa;1.2");  s.addstack("bbb;1.7;");  s.addstack("ccc;2.2");  s.parse();  // gives unhandled expression error   s.popstack();   s.printstack();  return 0; } 

the end of token found, in case ';', replaced 0.

this write operation done on string literal pass:

s.addstack("aaa;1.2"); 

but literal not writable, 'const char *', hence access violation.