Extract a floating point number from a CString

Question

I want to extract a floating point number from a CString formatted as: (example extract 22.760348)

Incidence_angle(inc)[deg]                 :22.760348

Basically I am reading a plain text file containing some parameters, and I want to perform some calculations on the values. I read the file using a CStdioFile object and extracting each line using the readString method as follows:

CStdioFile result(global::resultFile,CFile::modeRead);
while( result.ReadString(tmp) )
            {
                if(tmp.Find(L"Incidence_angle(inc)[deg]") != -1)
                {
                    //extract value of theeta i here
                    // this is probably wrong
                    theeta_i = _tscanf(L"Incidence_angle(inc)[deg]  :%f",&theeta_i);
                }
            }

I tried using scanf because I couldnt think of any other way.

I apologize if this question seems very basic and stupid, but I have been stuck on it for a long time and would apppriciate some help.

edit: took out the proof of concept program I wrote, caused confusion

Answer 1

_tscanf() returns the number of assignments made, not the value read:

theeta_i = _tscanf(L"Incidence_angle(inc)[deg]  :%f",&theeta_i); 

so theeta_i will contain 1 ( .0 ) if a float was successfully read. Change to:

if (1 == _tscanf(L"Incidence_angle(inc)[deg]  :%f",&theeta_i))
{
    /* One float value successfully read. */
}

---

That should be _stscanf() to read from a buffer, _tscanf() will be waiting for input from standard input.

Answer 2

Assuming that tmp is CString , the correct code is

CStdioFile result(global::resultFile,CFile::modeRead);
while( result.ReadString(tmp) )
{
if (swscanf_s(tmp, L"Incidence_angle(inc)[deg]  :%f", &theeta_i) == 1)
    {
        // Use the float falue
    }
}

Answer 3

Why not use atof ?

Example taken from the link:

   /* atof example: sine calculator */
    #include <stdio.h>
    #include <stdlib.h>
    #include <math.h>

    int main ()
    {
      double n,m;
      double pi=3.1415926535;
      char szInput [256];
      printf ( "Enter degrees: " );
      gets ( szInput );
      n = atof ( szInput );
      m = sin (n*pi/180);
      printf ( "The sine of %f degrees is %f\n" , n, m );
      return 0;
    }

Answer 4

Why not do it the C++ way altogether?

This is just a hint:

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

int main()
{
   double double_val=0.0;
   std::string dump("");
   std::string oneline("str 123.45 67.89 34.567"); //here I created a string containing floating point numbers
   std::istringstream iss(oneline);
   iss>>dump;//Discard the string stuff before the floating point numbers
   while ( iss >> double_val )
   {
      std::cout << "floating point number is = " << double_val << std::endl;
   }
   return 0;
}

If you want to use as you have illustrated, using cstring only, try strtod() also. Source: man -s 3 strtod