How to read groups of integers from a file, line by line in C++
I have a text file with on every line one or more integers, seperated by a space. How can I in an elegant way read this with C++? If I would not care about the lines I could use cin >>, but it matters on which 开发者_JAVA技巧line integers are.
Example input:
1213 153 15 155
84 866 89 48
12
12 12 58
12
It depends on whether you want to do it in a line by line basis or as a full set. For the whole file into a vector of integers:
int main() {
std::vector<int> v( std::istream_iterator<int>(std::cin),
std::istream_iterator<int>() );
}
If you want to deal in a line per line basis:
int main()
{
std::string line;
std::vector< std::vector<int> > all_integers;
while ( getline( std::cin, line ) ) {
std::istringstream is( line );
all_integers.push_back(
std::vector<int>( std::istream_iterator<int>(is),
std::istream_iterator<int>() ) );
}
}
You could do smtng like this(I used cin, but you can use any other file stream):
string line;
while( getline( cin, line ) )
{
istringstream iss( line );
int number;
while( iss >> number )
do_smtng_with_number();
}
Or:
int number;
while( cin >> number )
{
do_smtng_with_number();
}
What result do you want? If you want all the integers in a single vector, you could do something like:
std::ifstream input("input.txt");
std::vector<int> data(std::istream_iterator<int>(input),
std::istream_iterator<int>());
That discards the line-structure though -- you end up with the data all together. One easy way to maintain the original line structure is to read a line with getline, initialize a stringstream with that string, then put the values from that stringstream into a vector (and push that onto the back of a vector of vectors of int).
std::vector<std::vector<int> > data;
std::vector<int> temp;
std::string t;
while (std::getline(input, t)) {
std::istringstream in(t);
std::copy(std::istream_iterator<int>(in),
std::istream_iterator<int>(),
std::back_inserter(temp);
data.push_back(temp);
}
Here you go :
void readFromFile(string filename)
{
string line;
ifstream myfile(filename);
if (myfile.is_open())
{
while ( getline(myfile,line) )
{
cout << line << '\n';
}
myfile.close();
}
}
int main(int argc, char* argv)
{
readFromFile("Input.txt");
getchar();
return 0;
}
精彩评论