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:

#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;
	}
				
}

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:

[string strigToFind1 = "numb[";

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.

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:

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

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;
	}
				
}

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

Code:

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;
	}

   }				
}

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;
	}
				
}

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 
*/

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:

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