C++ getline to ignore comments "//"

[legcramp]

while(getline(infile,lines)) 
	{

		if(lines.empty())  
			{
				continue;
					
			}
		if(lines.find("//") == true)
			{
				continue;
			}
		
		++linecount;

I got the counter to skip spaces flawlessly, but skipping the comments in the line count isn't going very well.

Any help is appreciated!

 

[rflcptr]

edit: nvm

 

[legcramp]

Sorry, forgot to mention that I just want the counter to skip the line if the "//" is in front of the line.

Right now, the line is skipped for example:

cout << "Hello World" << endl; //comment here


But I only want it to skip the line if:

//comment here ...........

 

[BinarySynapse]

The find method seems to be looking for the substring anywhere in the string and returning a true value (presumably the position where it was found). If that's not the behavior you want, then you'll have to use a method that does what you need.

 

[Blazestorm]

Meh, try this... was bored. I assume this is some sort of "count lines of code" program... running this program on this cpp file returns 30 lines

Your "empty" check failed if they had random spaces/tabs on the line

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

unsigned count_lines( std::string const& filepath )
{
  unsigned linecount = 0;
  const std::string whitespace(" \t\n\r");
  std::string lines;
  std::ifstream infile( filepath );
  
  while( std::getline( infile, lines ) ) 
  {
    std::size_t first_nonws = lines.find_first_not_of( whitespace );
    
      // skip empty lines
    if( first_nonws == std::string::npos ) {
      continue;
    }
      // skip c++ comments
    if( lines.find("//") == first_nonws ) {
      continue;
    }
      // skip preprocessor directives (doesn't work on multiline)
    if( lines.find("#") == first_nonws ) {
      continue;
    }

    ++linecount;
  }
  return linecount;
}

int main( int arg_c, char** arg_v )
{
  if( arg_c == 2 )
  {
    std::cout << count_lines( arg_v[1] ) << std::endl;
  }
  return 0;
}

 

[Dogs]

while(getline(infile,lines)) 
	{

		if(lines.empty())  
			{
				continue;
					
			}
		if(lines.find("//") == true)
			{
				continue;
			}
		
		++linecount;

I got the counter to skip spaces flawlessly, but skipping the comments in the line count isn't going very well.

Any help is appreciated!

In your while loop:

if(lines.find("//") == true)

This line is not doing what you think it is. Find is not going to return a bool, but rather a size_t. size_t is an integer representing the index in the string where the match is found.

Since it isn't a bool, when you do compare it with a bool it is implictly converted into a bool before the comparison is made. When this happens, 0 becomes false and anything other than zero becomes true.

If a line begins with "//", when you do lines.find("//") it's going to return zero, which is going to be converted to false. If "//" appears anywhere else, it will return that position, which is true, or if it doesn't appear it will return -1 (std::string::npos), which is also true.

Therefore, if the string begins with "//", lines.find("//") is going to be false, and if it doesn't start with "//", lines.find("//") is going to be true. If you invert your logic and change it to "if (lines.find("//") == false)" it should work, but for clarity and understanding I would encourage you to compare actual values, so "if (lines.find("//") == 0)" rather than leaving a misleading expression in your code.

 

[Arainach]

You need to decide what behavior you really want, and write some code to parse it as appropriate. Is it OK if there's whitespace before the //? If so, you need to account for that.

Part of it depends on what you want to do - if you're trying to actually parse a file into some meaningful syntax, it may be worth looking into doing a proper token-based parser/lexer; there are plenty of tools out there to make that process simple.

 

[legcramp]

Thanks everyone, I ended up counting semi-colons instead for a logical lines of code count.

 

[Blazestorm]

Hmm, I don't think that's quite accurate, but if that's what you're going for...

  for(;;);

Which would have 3 lines of code counted, in reality it's 1 or 0... and useless (just putting an example out there)

  while( ( Node* node = FindNextNode() ) && node->value == 27 ) {
  }

Would count as 0 lines of code, because there's no semi-colons.

The only thing you need to add to my implementation is check for lines with just curly braces and you would have covered almost everything...

Or you could use cloc?