Exception with ::tolower

I am trying to read a .txt file and search for a number that is inside two brackets like this (Inside "Numb[?]")

What I also is doing is to transform all characters to lowercase and this I do inside the while loop. When I do this my program throws an exeption when running.
If I dont use a while loop and would manually put a string to the string Line then this will work.
Why could this happen when I use a while loop.

Code:

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#include <ctype.h>

std::string Line;
string stringToFind1 = "Numb[";

while( getline(fin1, Line, '\n')  )

{
std::transform(Line.begin(), Line.end(), Line.begin(), ::tolower);
string::size_type startPos = Line.find(stringToFind1);
startPos += stringToFind1.length();
string::size_type endPos = Line.find("]", startPos);
string Number = Line.substr(startPos, endPos - startPos);
       
        if( Line.find(stringToFind1) != string::npos )
        {
                fout1 << Number;
        }
                               
}

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If it's all lowercase, how will you find "Numb["?

yes you are right. It could also be like this. So in the above case I shouldn´t find it but in this case I will then but strange is that this while loop throws an exception. I cant really get it what it is.
Even if I will // the first line in the while loop that contains std::transform, I will get the exception.

Code:

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[string strigToFind1 = "numb[";

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Quote:

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Originally Posted by Coding

yes you are right. It could also be like this. So in the above case I shouldn´t find it but in this case I will then but strange is that this while loop throws an exception. I cant really get it what it is.
Even if I will // the first line in the while loop that contains std::transform, I will get the exception.

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Doesn't commenting out the transform further the case that the exception is elsewhere? Such as doing math on an error condition?

Do all your lines have numb[ in them? Otherwise startPos is out of range.

Check to make sure the result of your find() call isn't string::npos, don't just assume that the result is valid.

>> Check to make sure the result of your find() call isn't string::npos, don't just assume that the result is valid.

I think my problem is somewhere here. If my .txt file contains only lines with text without any blank lines beween. Then the code works but if I change so there is a blank line in the text file then I get the exception.

I thought this code took this into considiration but perheps I am wrong ?

Code:

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if( Line.find(stringToFind1) != string::npos )
        {
                fout1 << Number;
        }

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Playing it in my head, I see something like this:

Code:

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while( getline(fin1, Line, '\n')  )

{
std::transform(Line.begin(), Line.end(), Line.begin(), ::tolower);
string::size_type startPos = Line.find(stringToFind1);
startPos += stringToFind1.length(); // BANG!!!!
string::size_type endPos = Line.find("]", startPos);
string Number = Line.substr(startPos, endPos - startPos);
       
        if( Line.find(stringToFind1) != string::npos ) // safety check
        {
                fout1 << Number;
        }
                               
}

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Yes, you are right. I changed the code to this to make sure the string is not emty.
Thanks for your help...

Code:

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while( getline(fin1, Line, '\n')  )
{
  if( Line != "")
  {
 
  std::transform(Line.begin(), Line.end(), Line.begin(), ::tolower);
  string::size_type startPos = Line.find(stringToFind1);
  startPos += stringToFind1.length();
  string::size_type endPos = Line.find("]", startPos);
  string Number = Line.substr(startPos, endPos - startPos);
       
        if( Line.find(stringToFind1) != string::npos ) // safety check
        {
                fout1 << Number;
        }

  }                               
}

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Quote:

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Originally Posted by Dave_Sinkula

Playing it in my head, I see something like this:

Code:

---

while( getline(fin1, Line, '\n')  )

{
std::transform(Line.begin(), Line.end(), Line.begin(), ::tolower);
string::size_type startPos = Line.find(stringToFind1);
startPos += stringToFind1.length(); // BANG!!!!
string::size_type endPos = Line.find("]", startPos);
string Number = Line.substr(startPos, endPos - startPos);
       
        if( Line.find(stringToFind1) != string::npos ) // safety check
        {
                fout1 << Number;
        }
                               
}

---

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Actually, I think the BANG might belong two lines lower. (I know C requires implementations to handle unsigned overflow as wraparound without a signal, but maybe C++ is different.) But the point is, you need to stop just as soon as you find npos, which is right there on line 2.

I am not really sure if I follow. To find npos, I think meens to find the end of the string ?

I dont think my solution is the right approach even that it works. I am not sure wich line is, line 2.
Is it something I am doing wrong in the code that it cant handle blank lines.

My play code:

Code:

---

#include <iostream>
#include <fstream>
#include <string>

int main()
{
  std::ifstream file("file.txt");
  const std::string stringToFind1 = "Numb[";
  std::string Line;
  while ( std::getline(file, Line) )
  {
      std::string::size_type startPos = Line.find(stringToFind1);
      if ( startPos != std::string::npos )
      {
        startPos += stringToFind1.length();
        std::string::size_type endPos = Line.find("]", startPos);
        if ( endPos != std::string::npos )
        {
            std::string Number = Line.substr(startPos, endPos - startPos);
            if ( Line.find(stringToFind1) != std::string::npos )
            {
              std::cout << Number << '\n';
            }
        }
      }
  }
  return 0;
}

/* file.txt
df dNumb[123]df

asdf asd fa Numb[456]  dv df asdf

Numb[456]  dv df asdf

asdf asd fa Numb[456]
asdf asd fa Numb[456 5654a ]
asdf asd fa Numb[456

*/

/* my output
123
456
456
456
456 5654a
*/

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The general idea: make sure you've found something before you operate on what you've found.

Thanks... I think I undestand now.
The magic thing is to check that this to make sure you are handling the correct string.
This worked great.

Code:

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if ( startPos != std::string::npos )
if ( endPos != std::string::npos )

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