Parse the Contents of String Array C++

Question

Hi,

I've read a file, and stored its contents into a string array.

I need to change some numerical values, interpreted as characters by the compiler.

The file is of the format: ABCDE,EFGHIJ KLMNOPQRS,45.58867,122.59750

I've searched and studied but haven't got onto anything too comprehensive.

If someone can please tell me how to do this I would be very glad.

And I'm not allowed to use strtod; I think it's a C function and my program needs to be strictly C++ only.

Here is my code that I've developed so far:

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <iomanip>
#include <cstdlib>
#include <sstream>


using namespace std;


int main()
{

    string usrFileStr,
    fileStr = "airNames.txt",  // declaring an obj string literal
    sBuffer,
    sLine = "";

    istringstream iStrStrm;

    int lineCount = 1;
    int nStart;


    fstream inFile;                  // declaring a fstream obj
    // cout is the name of the output stream
    cout << "Enter a file: ";
    cin >> usrFileStr;


    inFile.open( usrFileStr.c_str(), ios::in ); 
    // at this point the file is open and we may parse the contents of it


    while ( getline ( inFile, sBuffer ) && !inFile.eof() )
    {
          nStart = -1 ;
          cout << "First Str " << lineCount << " (";
          for ( int x = nStart + 1; x < sBuffer.length(); x++ )
          {
              if ( sBuffer[ x ] == ',' )
              {
                   nStart = x;
                   break;
                   }
              cout << sBuffer[ x ];


          }
          cout << ") ";
          for ( int x = nStart + 1; x < sBuffer.length(); x++ )
          {

              if ( sBuffer[ x ] == ',' )
              {    
                   nStart = x;
                   break;
                   }
              cout << sBuffer[ x ];
          }
          cout << " (Second Str: "; // lattitude loop


          for ( int x = nStart + 1; x < sBuffer.length(); x++ )
          {
              if ( sBuffer[ x ] == ',' )
              {
                   nStart = x;
                   break;
                   }
              cout << sBuffer[ x ];         
          }

          cout << ", Third String: ";
          for ( int x = nStart + 1; x < sBuffer.length(); x++ )
          {
              if ( sBuffer[ x ] == ',' )
              {
                   nStart = x;
                   break;
                   }
              cout << sBuffer[ x ];
          }
          cout << ") \n";
          lineCount++;
    }


    cout << "There are a Total of: " <<  lineCount << " line(s) in the file."
    << endl;


    inFile.clear();           // clear the file of any errors
    inFile.close();  // at this point we are done with the file and may close it

    fgetc( stdin );
    return 0;
}

I've tried to only read two digits after the decimal, but I only get one character. My first attempt was with static_cast but that was way off. And a istringstream variable won't let its argument be an array. I don't know what to do..

Answer 1

stringstream

Learn to love it. Not istringstream, since you want to get output from it. Something like:

getline ( inFile, sBuffer );
stringstream myStream(sBuffer);
string first, second, third;
char comma;

myStream >> first;  
myStream >> second;
myStream >> third;

float value1, value2;
myStream >> value1;
myStream >> value2;

Also I would advise you check to make sure the file actually opens.

Answer 2

You want stringstream, as suggested, but...

As an aside, it's silly to neglect C functions in the context of a C++ program. Most OS functions are going to be exported as C functions, and C++ itself is generally (always?) compiled down to the equivalent of C code anyway, so there's nothing that sticking to only C++ constructs/functions buys you. By all means use the higher-level abstractions and methodologies provided by C++ when appropriate, but if you try to avoid all C-linkage functions, you're hurting yourself for no good reason. Use what works; real programming is hard enough without jumping through self-imposed limitations.

Of course, the above is only applicable to real world programming; homework assignments and such may be the exception. :)

Answer 3

Hi,

You can also try to use boost regex, See: http://www.boost.org/doc/libs/1_37_0/libs/regex/doc/html/boost_regex/captures.html

This way you can add a reqex for the ',' char and capture the values within, even validate them maybe...

Good luck !

Answer 4

Using string.find() could get rid of some of your loops (it probably just does them internally, but no need to reinvent the wheel). You can use a stringstream to convert the number strings into floats or doubles.

Answer 5

Use boost spirit (http://www.boost.org/doc/libs/1_37_0/libs/spirit/classic/index.html). Takes a moment to get used to but is very powerful and useful if you get to know it.