Using fstream getline () function inside a class
I am trying to load the lines of a text file containing dictionary words into an array object. I want an array to hold all words starting with "a", another one for "b" ... for all letters in the alphabet.
Here's the class I wrote for the array object.
#include <iostream>
#include <string>
#include <fstream>
using namespace std;
class ArrayObj
{
private:
string *list;
int size;
public:
~ArrayObj(){ delete list;}
void loadArray(string fileName, string letter)
{
ifstream myFile;
string str = "";
myFile.open(fileName);
size = 0;
while(!myFile.eof())
{
myFile.getline(str, 100);
if (str.at(0) == letter.at(0))
size++;
}
size -= 1;
list = new string[size];
int i = 0;
while(!myFile.eof())
{
myFile.getline(str, 100);
if(str.at(0) == letter.at(0))
{
list[i] = str;
i++;
}
}
myFile.close();
}
};
I am getting the error:
2 IntelliSense: no instance of overloaded function "std::basic_ifstream<_Elem, _Traits>::getline [with _Elem=char, _Traits=std::char_traits<char>]" matches the argument list d:\champlain\spring 2012\algorithms and data structures\weeks 8-10\map2\arrayobj.h 39
I'm guessing this requires me to overload the getline function, but I'm not entirely sure how to do this or why this is necessary.
Any advice?
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the function for streams that deals with std :: string is not an istream member function, but a free function that is used like that. (the member function version deals with char *).
std::string str;
std::ifstream file("file.dat");
std::getline(file, str);
It's worth noting that there are safer ways to do what you are trying to do like this:
#include <fstream>
#include <string>
#include <vector>
//typedeffing is optional, I would give it a better name
//like vector_str or something more descriptive than ArrayObj
typedef std::vector<std::string> > ArrayObj
ArrayObj load_array(const std::string file_name, char letter)
{
std::ifstream file(file_name);
ArrayObj lines;
std::string str;
while(std::getline(file, str)){
if(str.at(0)==letter){
lines.push_back(str);
}
}
return lines;
}
int main(){
//loads lines from a file
ArrayObj awords=load_array("file.dat", 'a');
ArrayObj bwords=load_array("file.dat", 'b');
//ao.at(0); //access elements
}
don't reinvent the wheel; control vectors are standard and will save you a lot of time and pain.
A final attempt not to insert using namespace std
, which is bad for a whole host of reasons I won't go in; instead, prefix std objects with std :: so like std :: cout or std :: string.
http://en.cppreference.com/w/cpp/container/vector http://en.cppreference.com/w/cpp/string/basic_string/getline http://en.cppreference.com/w/cpp/ string
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