Thread: Strings

try the strcpy( ) function.. it should copy the string to the char array all at once.

Code:

while(INPUTFILE && INPUTFILE.peek() != EOF)
{
  getline(INPUTFILE, theTerms);
  strcpy(s, theTerms.c_str());
}

You seem to be getting only one line at a time. Do you want the data to be available outside the loop?

If you only want a vector of tokens from the file (don't care where the lines end):

Code:

std::vector<std::string> tokens;
std::ifstream fin(...);
std::string input;
while (fin >> input) {
    tokens.push_back(input);
}

If you care about where each line ends, you might use a vector of vectors:

Code:

std::vector<std::vector<std::string> > tokenLines;
...
while (std::getline(fin, line)) { //preferable way of reading lines
     //tokenise
     //push resulting vector<string> onto tokenLines
}

Well this is just the file processing part of a larger program. I have gone through several different options for extracting data from the input file and have settled with using string streams since they seem to be more efficient.

So the input file would have lines like the following, where there could be any amount of whitespace within the terms or outside each line of the polynomials represented by:

2 : 3 1 2 1 4 2

4 : 5 2
2 = 2 * 4
display 2

Where the first integer followed by a colon denotes the location of the poly and the rest denote coefficient and exponent terms.

But I think that I found the cause of my problems. I read somewhere that stringstream can do both input and output. But when I changed it to an istringstream, things started to work as I intended them to work.

I have a question about istringstream. My inputfile has a line like:

show 2

and I have a string s and I assign it the string "show". I also have an int poly.

shouldn't this statement work?

Code:

if(iss >> show >> poly) 
{
  //do something
}

It ought to read the string into the variable show (which would then have the value "show") and the integer into poly (which would then have the value 2).

I am confused now because I have a line like:

2 : 3 2 1 0

and a char object called colon assigned with ':'

when I test the following block of code, everything works as I think and intend it to work.

Code:

if (iss >> poly >> colon)
{
  aInt = poly;
  
  while(iss >> coeff >> exp)
  { 
    ....

So is it is possible to check if an istringstream reads something in particular, as I am attempting to do? or, I am doing it incorrectly? Because it apparently works in one case and doesn't in another.

Well, what does it do in the case where it doesn't work, and what do you expect it to do?

Originally Posted by CornedBee

Well, what does it do in the case where it doesn't work, and what do you expect it to do?

Assuming the line is :

show 0

I expect the program to enter this block because the istringstream did indeed contain a line containing show and some integer. But it does not enter that block of code.

Code:

if(iss >> show >> poly) 
{
  //do something
}

This is one of the blocks inside a while loop that assigns one line of the file to the istringstream. I have ruled out a problem with the while loop or the assignment of the line to the istringstream because I checked to see what istringstream contained each time around.

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