[Jheshka]

How would I go about getting the amount of occurences that the char g appears in a file?

[PM]

You could do something like

#include <iostream>
#include <fstream>

int main(int argc, char* argv[])
{
   if (argc < 2)
   {
      std::cout << "Usage: countchars [filename]" << std::endl;
      return 1; 
   }

   std::ifstream file(argv[1]);
   
   if (file.bad())
   {
      std::cout << "Error opening file." << std::endl;
      return 1;
   }

   size_t count_g = 0;

   while (!file.eof())
   {
      if (file.get() == 'g')
         ++count_g;
   }

   std::cout << count_g << std::endl;

	return 0;
}

[joaquimandrade]

Originally Posted by PM You could do something like #include <iostream> #include <fstream> int main(int argc, char* argv[]) { if (argc < 2) { std::cout << "Usage: countchars [filename]" << std::endl; return 1; } std::ifstream file(argv[1]); if (file.bad()) { std::cout << "Error opening file." << std::endl; return 1; } size_t count_g = 0; while (!file.eof()) { if (file.get() == 'g') ++count_g; } std::cout << count_g << std::endl; return 0; }

And what about making the while like:

PHP Code:

   while (!file.eof())
       count_g += (file.get() == 'g') 


[PM]

Mmm, I guess it would compile and everything but (file.get() == 'g') is of the type bool in C++, some compilers will not like this, so it might be better to write

  while (!file.eof())
       count_g += (file.get() == 'g') ? 1 : 0;

[joaquimandrade]

Originally Posted by PM Mmm, I guess it would compile and everything but (file.get() == 'g') is of the type bool in C++, some compilers will not like this, so it might be better to write while (!file.eof()) count_g += (file.get() == 'g') ? 1 : 0;

My knowledge in C++ is limited to my knowledge in C,Java and C#. In Java it must be like you said.

[PM]

Actually IIRC bool is an integral type so it will get implicitly promoted to an int so the code you wrote should be no problem either.

BTW: file.bad() was wrong, use if (!file) instead.


EDIT:
If you want something cool, you could also do something like this:

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

template <class INT_TYPE, INT_TYPE WHAT>
class CGCounter
{
   size_t m_Count;
public:
   CGCounter() : m_Count(0)
   {
   }

   void operator () (INT_TYPE curElem)
   {
      if (curElem == WHAT)
         ++m_Count;
   }

   operator size_t () const
   {
      return m_Count;
   }
};

int _tmain(int argc, _TCHAR* argv[])
{
   if (argc < 2)
   {
      std::cout << "Usage: countchars [filename]" << std::endl;
      return 1; 
   }

   std::ifstream file(argv[1]);
   
   if (!file)
   {
      std::cout << "Error opening file." << std::endl;
      return 1;
   }

   std::cout << static_cast<size_t>(
      std::for_each(std::istream_iterator<char>(file), std::istream_iterator<char>(), CGCounter<char, 'g'>()))
      << std::endl;

	return 0;
}

istream_iterator<A> is a class which acts like a STL iterator and reads objects of type A from the stream.
for_each iterates from its first parameter to its second parameter (in this case istream_iterator<char>() constructs an interator which shows where to end ) and applies its third parameter on each element. Then it returns that third parameter again.
In this case the third parameter is CGCounter, a "functor", ie. a class which overloads operator() and thus looks like a function. You can specify what elements to count by specifying the type and the object to compare to in the template arguments (enclosed in < > ).
CGCounter also provides a conversion to size_t which simply returns the current counter value.

[Jheshka]

Thank you very much, PM

[joaquimandrade]

Originally Posted by PM Actually IIRC bool is an integral type so it will get implicitly promoted to an int so the code you wrote should be no problem either. BTW: file.bad() was wrong, use if (!file) instead. EDIT: If you want something cool, you could also do something like this: #include <iostream> #include <fstream> #include <string> #include <algorithm> template <class INT_TYPE, INT_TYPE WHAT> class CGCounter { size_t m_Count; public: CGCounter() : m_Count(0) { } void operator () (INT_TYPE curElem) { if (curElem == WHAT) ++m_Count; } operator size_t () const { return m_Count; } }; int _tmain(int argc, _TCHAR* argv[]) { if (argc < 2) { std::cout << "Usage: countchars [filename]" << std::endl; return 1; } std::ifstream file(argv[1]); if (!file) { std::cout << "Error opening file." << std::endl; return 1; } std::cout << static_cast<size_t>( std::for_each(std::istream_iterator<char>(file), std::istream_iterator<char>(), CGCounter<char, 'g'>())) << std::endl; return 0; } istream_iterator<A> is a class which acts like a STL iterator and reads objects of type A from the stream. for_each iterates from its first parameter to its second parameter (in this case istream_iterator<char>() constructs an interator which shows where to end ) and applies its third parameter on each element. Then it returns that third parameter again. In this case the third parameter is CGCounter, a "functor", ie. a class which overloads operator() and thus looks like a function. You can specify what elements to count by specifying the type and the object to compare to in the template arguments (enclosed in < > ). CGCounter also provides a conversion to size_t which simply returns the current counter value.

Yes, it is very cool. Just a thing: Wouldn't it be more correct to say, instead of: "ie. a class which overloads operator() and thus looks like a function" , "ie. a class on which the operator () is overloaded and thus can be used as function"? That because, the class still looks like a class.