Thread: Strings

Can you provide more code? What you posted works when put into a simple (and complete) program:

Code:

#include <iostream>
#include <string>
#include <sstream>

int main()
{
    std::istringstream iss("show 0");
    std::string show;
    int poly;
    if (iss >> show >> poly)
    {
        std::cout << "Success!\n";
    }
    else
    {
        std::cout << "Failure!\n";
    }
}

Here is the loop:

Code:

 int poly, argument, coefficient, exponent;
 char colon = ':';
 char assignment = '=';
 char multiply = '*';

 while(INPUTFILE && INPUTFILE.peek() != EOF)
 {
   getline(INPUTFILE, theTerms);
   iss.str(theTerms);
     
if(iss >> poly >> colon)
{
 locationOfPoly = poly;                   
   
   while(iss >> coefficient >> exponent)
   {
    tPoly.insert(exponent, coefficient);
   }

   //postcondition: all info has been extracted from iss so assign tmpPoly
   //to Poly[locationOfPoly] 
   Poly[locationOfPoly] = tPoly; 
}  
  
    
  if(iss >> poly >> assignment >> poly >> multiply >> poly)
   {
    Poly[poly] = Poly[poly] * Poly[poly];
   }
   
   if(iss >> show >> poly)
   {         
    locationOfPoly = poly;
    cout <<"Poly[" << locationOfPoly << "] = " << Poly[locationOfPoly] << "\n";
   }
 
 }//end while INPUTFILE loop

If the line is "show 0", then the first if statement will run and fail.

Code:

if(iss >> poly >> colon)

poly is an int, but "show" is not, so this causes a failed read. I think you are assuming that it will move on to the next if and try again, right? Unfortunately, when one failure happens it sets a failbit in the stream. you have to clear that failbit before trying again. You can do this by calling clear.

However, you stil might have a problem between the first and second if. Both start with an int, so if the line is meant for the second if, the first if might still read part of the data.

What I would do is re-set the istringstream after each if:

Code:

iss.clear();
iss.str(theTerms);

Thanks, that did it.

Originally Posted by Daved

If the line is "show 0", then the first if statement will run and fail.

Code:

if(iss >> poly >> colon)

poly is an int, but "show" is not, so this causes a failed read. I think you are assuming that it will move on to the next if and try again, right? Unfortunately, when one failure happens it sets a failbit in the stream. you have to clear that failbit before trying again. You can do this by calling clear.

However, you stil might have a problem between the first and second if. Both start with an int, so if the line is meant for the second if, the first if might still read part of the data.

What I would do is re-set the istringstream after each if:

Code:

iss.clear();
iss.str(theTerms);

I now realize that I was using the stringstream improperly and found that this was the cause of a major problem. Now I know and have learned that the variables in the if () conditions just accept a string, a char, or int in my case. So to do what I really wanted, I had to add an && condition to check if that variable actually contained what I was looking for.

char colon = ':';
char assignment = '=';
char multiply = '*';

The above was pointless since these would be replaced by what was read.