Question

i obtained a double value with decimal part as 0 from calculations and then want to convert this value into char array consisting of the digits as elements(using ascii codes) and then return it…i wrote the following code for it…

char* as_string(double a,char* ptr)
{
  int digits=0;
  for(int i=1;;i++)
  {if(static_cast<int>(a/pow(10.0,i))==0)
  {digits=i;
  break;}
  }

 char b[digits];
 for(int i=digits-1;i>=0;i--)
 {
 b[digits-1-i]=static_cast<int>(a/pow(10.0,i))+48;
 a=a-((b[digits-1-i]-48)*pow(10.0,i));
 }

 strncpy(ptr,b,digits);
 return ptr;
}     

everything went on all right…there was no syntax error but at runtime the prog was aboted each time…after some scrutiny i found that error is taking place around pointer ptr and strcpy statements(as the array b was successfully tested as filled with the digits )…can anyone plz. point out the error?

Answer 1

You should ask yourself the Question:

Is ptr pointing to a memory location big enough to hold digits?
I don’t think so.

The problem is you are passing a pointer ptr to the function but you don’t know before hand how much memory is needed to be allocated to ptr.

You can have two options:

You can guess the maximum value possible allocate the same to ptr using new or on stack & then pass ptr to the function

Or

You allocate memory to ptr inside the function using new where you know exactly how much memory is needed. Note that to do so you will have to pass ptr as a double pointer.