How can I read lines from file and cut it pieces? - c++

Question

[EDIT]
I specified my question, maybe it has more information:
I have a file with lots of lines like "string1 string2 int1 int2", so a line contains two strings and two integers. I would like to read the file line by line and push those four datas into a vector of my struct( which has the same variable types and num ). My question is, how can I do this, because the >> operator won't work anyway. Nor the getline().
and the code:
void FromFile(string filename)
{
ifstream stream;
stream.open(filename);
adatok adattemp;
while(stream.good())
{
stream >> adattemp.agresszor >> adattemp.vedo >> adattemp.haborukezdete >> adattemp.haboruvege >> ws;
cout << adattemp.agresszor;
vektor.push_back(adattemp);
}
stream.close();
}

Answer 1

Assuming each string is just a single word, this should work:
#include <vector>
#include <string>
#include <fstream>
struct Entry {
std::string s1;
std::string s2;
int i1;
int i2;
};
std::vector<Entry> entries;
int main()
{
std::ifstream file("yourfile");
while (file.good()) {
Entry entry;
file >> entry.s1 >> entry.s2 >> entry.i1 >> entry.i2 >> std::ws;
entries.push_back(entry);
}
return 0;
}
Note: it's important to include >> std::ws at the end of reading each line. It eats up extra whitespace. Otherwise you'll end up with an extra junk entry at the end of the file.
EDIT: As Simple pointed out in the comments, if any errors occur while reading the file, the above code will store a junk entry at the end of the vector. This code will fix that by making sure there are no errors before storing the entry:
Entry entry;
while (file >> entry.s1 >> entry.s2 >> entry.i1 >> entry.i2 >> std::ws)
{
entries.push_back(entry);
}

Answer 2

I'd overload >> and use std::copy
#include<vector>
#include<algorithm>
//...
struct Reader {
std::string str1;
std::string str2;
int int1;
int int2;
friend std::istream& operator << (std::istream& is, Reader &r)
{
return is >> r.str1 >> r.st2 >> r.int1 >> r.int2 ;
}
};
std::vector<Reader> vec;
std::ifstream fin("file_name");
std::copy(std::istream_iterator<Reader>(fin),
std::istream_iterator<Reader>(),
std::back_inserter(vec)
) ;
This assumes all string and int are seperated by white space
You can also overload >> too to display content in similar fashion

Answer 3

Since you do not know the file size, a vector would be more suited IMO.
while ( myFile >> string1 >> string2 >> myInt1 >> myInt2 ) {
stringvec1.push_back( string1 );
stringvec2.push_back( string2 );
intvec1.push_back( myInt1 );
intvec2.push_back( myInt2 );
}
EDIT:
If the 4 variables that you are reading correspond to a particular logically meaningful class, then you can have one vector of class/struct with all these 4 as members.
Something like:
struct myFileVariables {
std:string m_string1;
std:string m_string2;
int m_myInt1;
int m_myInt2;
myFileVariables ( string string1, string string2, int myInt1, int myInt2 ) :
m_string1( string1 ), m_string2( string2 ), m_myInt1( myInt1 ),
m_myInt2( myInt2 ) {}
};
And in your main function:
while ( myFile >> string1 >> string2 >> myInt1 >> myInt2 ) {
myFileVariables newEntry( string1, string2, myInt1, myInt2 );
myVec.push_back( newEntry );
}